My 1969 ts 250 is burning crank case oil. Must be the crankshaft seal is out? Can I replce the seal without spliting the crankcase joint?

Probable crankcase leak... most likely the crankshaft seals, but can be crank case seal or head to case seal or all. Web search "stihl chainsaw crankcase leak" for help.

Unfortunately the comprehensive tests for a crankcase leak is not a simple task and involves significant disassembly. Get a visual on the crank seals and go from there.

if there is a faulty seal on the crankshaft then the gear oil can get to the crankcase
being a separate case with separate oil, check that the breather for the transmission is not blocked and the pressure build up is not forcing the oil past the seal into the crankcase

Idling high on start up sounds like a blown crank seal. Check for any oil around the seals on each end of the crankshaft, they should be bone dry. Replacing them doesn't require splitting the crank cases.

DT yamaha,s are a 2 stroke, the oil is pumped into the engine and burnt with the fuel, at aproximately 30-1 ie: every 30 litres of fuel will burn 1 litre of oil, this is how the engine gets its lubrication , without it the engine will be destroyed, they also have gearbox oil which only lubes the gears and clutch

In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder(s), which in a multicylinder engine are usually integrated into one or several cylinder blocks. Crankcases have often been discrete parts, but more often they are integral with the cylinder bank(s), forming an engine block. Nevertheless, the area around the crankshaft is still usually called the crankcase. Crankcases and other basic engine structural components (e.g., cylinders, cylinder blocks, cylinder heads, and integrated combinations thereof) are typically made of cast iron or cast aluminium via sand casting. Today the foundry processes are usually highly automated, with a few skilled workers to manage the casting of thousands of parts.
A crankcase often has an opening in the bottom to which an oil pan is attached with a gasketed bolted joint. Some crankcase designs fully surround the crank's main bearing journals, whereas many others form only one half, with a bearing cap forming the other. Some crankcase areas require no structural strength from the oil pan itself (in which case the oil pan is typically stamped from sheet steel), whereas other crankcase designs do (in which case the oil pan is a casting in its own right). Both the crankcase and any rigid cast oil pan often have reinforcing ribs cast into them, as well as bosses which are drilled and tapped to receive mounting screws/bolts for various other engine parts.
Besides protecting the crankshaft and connecting rods from foreign objects, the crankcase serves other functions, depending on engine type. These include keeping the motor oil contained, usually hermetically or nearly hermetically (and in the hermetic variety, allowing the oil to be pressurized); providing the rigid structure with which to join the engine to the transmission; and in some cases, even constituting part of the frame of the vehicle (such as in many farm tractors).

1. Oil plug gasket 2. clutch cover gasket, 3. Center case leaking
4. TOO much oil in crankcase, 5. Shift shaft seal. 6 Counter shaft seal.

There is a crankcase vent on top that may be cracked or out of place causing the oil to leak or the upper crankshaft seal may be leaking.

There are two places where gearbox oil can leak into the combustion process: from the gasket between the two engine case halves, or from the crank seal on the right hand end of the crankshaft. The most likely culprit is the crankshaft seal.

Assuming all screws are out, intake, exhaust and cylinder, oil pump and all oil pump related items are removed Screw the clutch carrier back on to the crankshaft (this protects the crank threads) and tap the crankshaft with a brass hammer. (TAP not Whack.) The tapping should loosen the 2 halve of the crankcase. You must replace the crankcase gasket.

did you check the pulley on the crank shaft ??
is it warped ?? ( bent )
because i do not think that the truck will run with the crankshaft moving.....back and forth.
so in any case you have a lot of work to do.
here is how to remove the crank shaft.
REMOVAL

1. Remove the oil pan.
2. Remove the oil pump from the rear main bearing cap.
3. Remove the vibration damper.
4. Remove the timing chain cover.
5. Identify bearing caps before removal. Remove bearing caps and bearings one at a time.
6. Lift the crankshaft out of the block.
7. Remove and discard the crankshaft rear oil seals.
8. Remove and discard the front crankshaft oil seal.

INSTALLATION

1. Lightly oil the new upper seal lips with engine oil.
2. Install the new upper rear bearing oil seal with the white paint facing towards the rear of the engine.
3. Position the crankshaft into the cylinder block.
4. Lightly oil the new lower seal lips with engine oil.
5. Install the new lower rear bearing oil seal into the bearing cap with the white paint facing towards the rear of the engine.
1. Apply 5 mm (0.20 inch) drop of Loctite 518, or equivalent, on each side of the rear main bearing cap. DO NOT over apply sealant or allow the sealant to contact the rubber seal. Assemble bearing cap to cylinder block immediately after sealant application.
2. lb align the bearing cap, use cap slot, alignment dowel and cap bolts. DO NOT remove excess material after assembly. DO NOT strike rear cap more than 2 times for proper engagement.
3. Clean and oil all cap bolts. Install all main bearing caps. Install all cap bolts and alternately tighten to 115 Nm (85 ft. lbs.) torque.
4. Install oil pump.
5. Install the timing chain cover.
6. Install the vibration damper.
1. Apply Mopar Silicone Rubber Adhesive Sealant, or equivalent, at bearing cap to block joint to provide cap to block and oil pan sealing. Apply enough sealant until a small amount is squeezed out. Withdraw nozzle and wipe excess sealant off the oil pan seal groove.
2. Install new front crankshaft oil seal.
3. Immediately install the oil Dan.

if you have an email address i can send some images