C240 w202 2000 oil leaking from filter, am i able to just put a new filter on without upsetting any sensors? As its quite a bad leak, think the o-ring might have loosen off maybe...

what was entailed in the rebuild?
cylinders bored and hone , new pistons , rings
crank grind and new bearings
or was it just a ring refresh and sand paper on the cylinders
I'm thinking the latter ( cheap and nasty)
The oil will be coming past the rings and being burnt in the exhaust ( cat converter if you still have one )
That oil passing the rings comes from , glazed bores , rings being installed upside down, ring gaps not being set 120 degrees apart but almost lining up
worn ring lands in the pistons
Sump oil either leaks out -- Gaskets , seals filters or is passed by the rings and burnt in the combustion process

Perhaps but it could also be a bad oil filter seal. Might want to remove the filter to inspect both the seal and the housing.

Check the oil filter. The old gasket might be stuck on the engine (two gaskets stuck together), or the new gasket might be defective, misaligned or missing.

I really doubt that the oil filter housing could be cracked by having a new filter put on. The spin on filter's sealing "O" Ring was probably pinched or left off or mis-aligned causing it to leak. With the proper "O" Ring, and seated correctly the spin on filter only has to be hand tight. If it is leaking, take it back and complain.

I suspect that some how the spin on filter has been knocked loose and disturbed the integrity of the "O" Ring seal, or the spin on filter was put on wrong and pinched the "O" Ring seal. You will have to try a new filter and "O" Ring, which means draining the oil and replacing. When fitting a new "O" Ring to a new filter, be sure that the ring fits perfectly in the slot. Coat the "O" Ring with some vasoline to hold it n place. If the "O" Ring will not fit flat in the grove heat the "O" Ring in a pan of hot water for about two minutes. This will relax the ring and take out any folds.



















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could be a split in the o ring on the filter just buy new filter they are cheap, take old oil rub new ring down and put new filter on hand tight nothing more.

Raise the car.
Put a pan the holds at least 2 gallons under the oil plug
Loosen and remove the bolt in the very bottom of the oil pan and remove; the oil will flow out and into the pan.
Clean and replace the oil plug, tightening it snug. the plug has no load on it, you don't have to tighten it really tight. Tight enough to stay in and seal against the oil is all that's required. Of course, you also want to enure it doesn't fall out...
Unscrew the oil filter. (Use the appearance of the new one you bought as a guide for what you are looking for.) The filter is often difficult to remove. There are special tool for removing them — you should probably get one. DO NOT USE AN OIL FILTER WRENCH TO INSTALL THE NEW FILTER.
Dump the oil ou of the old filter sufficiently to handle it without sloshing.
Put the mounting surface of the new filter and the old filter together to ensure that the rubber rings are the same. Better to find out you have the wrong filter now that after you screw it on, and have your new oil leak out.
Pour some of the new oil into the new filter. Starting the engine will fill it up, but the longer it takes to fill, the longer the engine runs without a good supply of oil. The pre-filling you do shortens that period.
screw the new filter into place. Carefully find the point where the rubber sealing ring makes contact, and tighten the filter 1/4 turn farther. Do not over-tighten the filter.
Remove the oil filler cap on the top of the engine, and pour in 5 quarts of oil.
Look to ensure no oil is leaking. I once forgot to replace the oil plug and poured 5 Qts trough the engine onto the ground. That is bad enough. But if I had not checked before I started the engine I might have destroyed the engine as well..
Check the oil dipstick to ensure you have enough oil in the engine.
If no leaks, and enough oil on the stick, start the engine without using the gas pedal — just let it rise to an idle on its own.
Look under the car for any leaks. If the oil filter is the wrong one, or is improperly installed it will leak right away.
If no leaks after 1 or two minutes, lower the car and shut the hood.

Please dispose of the used oil responsibly.

if oil filter was replaced and now leaks need to get new one and make sure you put a little oil on your finger and rub it on the rubber gasket on new filter and only tighten hand tight.

Nope, just replace the oil filter. The filter may be loose or if the oil filter was placed without oil on the O-ring before installation will cause the O-rings to fail. If the car is due for an oil change, might as well service the engine and replace the oil and filter. Good luck and hope it's not the oil pressure sensor which will leak when it fails too and it's most of the time located by the oil filter area in most cars.

If you had the oil changed lately and the "O" ring stuck where the filter unscrews and someone proceeded to put the new filter on without looking this can cause a problem. Putting too much oil in the crankcase can cause a seal to blow. A leak at the oil pressure switch. A loose or not sealed oil drain plug. You will need to try to locate whether it is coming from the bottom or at the top around the valve pan cover which is the most likely place, and if it that is the case; it still can drip through the night while it sets, which is missleading. If you can't find any noticeable places...that is a good place to start...at the valve pan cover...seal it real well with RTV sealer, let it dry over night and see if the problem goes away.