Need to replace old one it has a hole in it and it rusting

Hi Merre:
Sure, blame the kid.
Easiest fix would be to cut out the section where the hole is and install a piece of flexible tubing. CAUTION! Gas is extremely flammable. Use appropriate tools (NOT a Zip Cutter).
Best fix would be to replace fuel line.
I'd suggest that youcheck with a parts supply to see if appropriate gas lines are available. You may need to use a flaring tool if you have to "custom build" the line.
It's OK kid, the cars is 15 years old and the line was probably rusted.
Cheers.

Note how far the plug is recessed in its hole. You will want to tap in the new plug to the same depth.
Use a hammer and small punch. Put the punch at the edge, not on the lip of plug, but out near the edge. Tap on it until it starts moving inward, the opposite side will be pushed out. Grab onto it with a pair of pliers and wiggle it out of the hole.
Clean the recess of rust and dirt, place the new plug in and tap it in evenly to the depth of the old plug. It may help to use a socket that fits inside the plug as a driver to drive it in evenly.

Keep an eye on the other freeze plugs. When one rusts through, others may follow. You should drain all the old coolant out, flush the engine and radiator, and put in new coolant, new thermostat too is a good idea. If rust is bad, consider a professional flush-they can do a much better job than a garden hose. Your radiator may need attention, too.
Good luck.

If you are a panel beater or good welder it will be an easy fix. Cut out the rust and replace it with a piece of panel metal ( from an old door -any old car door)

OLD CAR. Depends how bad the rust is, do you need new panels or can you fill the holes themselves with filler ? Main thing is would it pass a MOT Test. Japanese Cars in the 70s & 80s were made from recycled steel, they were all prone to rust.

IF it has an o-ring seal drop a little oil on it, use a twisting motion when seating it, you may have a reflector/flywheel that is out of spec.OEM part number should be 4609009. Installation pretty straight foward.

Considering your car is only worth $5,000 in great shape, I don't think it is worth repairing a rusted out frame and under body. If it was a 72, I would say yes, but 81, ahh, My brother used to restore cars, I saw what he went through, buying and selling his cars, He stopped buying rust buckets, if they had one spec of rust, he didn't touch it, there are plenty of rust free cars out there, And repairing rust is a nightmare, your Mercedes is not like a Chevy where they have every panel in stock ready to weld in, You would need to hire a body man full time for a year to get those panels fixed back up, and get it done on the frame??? Forget it, the frame is probably shot. Painting the undercarriage will take most of your money, you will never get it back out of the car. Hope this helps.

That will be very difficult to find. Your best bet would be take it to an auto body shop. and have them treat the rust and weld a panel over the old one and treat it with rust proofing. if you plan on keeping it for a long while.

If the water seems to be coming out of the engine block itself it would be the welch plugs. To actually see them you either need detachable eyes or a flashlight and a small mirror. Welch plugs are brass plugs inserted into holes in the engine block. These holes were put there during manufacturing in order to clear the sand used in the casting process from the water channels. They do tend to rust through and replacing them can be a serious headache due to the diffyculty in accessing these plugs. Basically you would have to strip everything(ancilliary components, inlet, exhaust manifold) off the engine to replace one. It can be removed by hammering a screwdriver through one and wedging it out. Replacement entails using a circular drift to hammer it back in (after the hole has been cleared of rust)
Also bear in mind that if one is rusted through, then the others are not far behind. depending on the engine it could have any number from 4 to 10 of these in the sides of the block alone.
The picture shows a welch plug (circled) on a 26 year old Nissan without aircon, power steering or fuel injection and it is still the only one visible on the engine without removing components.

make sure there is no material from the old plug left in the hole. clean inside hole with light grade emory cloth. put some hi-temp sealer on the mating surface of the plug. tap into place hollwed side out, edge flush with the engine surface. measure the hole precisely to get the correct size plug. access to hole may be limited.

if the pump is leaking then it needs replacing it sounds like someone in the past has introduced glycol based coolant in to a oat. organic acid tech coolant system THEY DO NOT MIX and go like brown jelly and block things up like heater/ac systems it needs a good flush using a cooling system flushing adative