Question regarding Oil leaks while under pressure M103
 

This is a question regarding my 89 300E.

My car has always gone through some oil. I've never been able to really pinpoint it, but I would be putting in a quart roughly every fillup. I have changed the valve cover gasket, and I know it is coming from somewhere at the rear of the engine. The valve cover is sealing, even at the back half-moon area (this was my first suspect). Over the last couple of weeks, I've noticed that I am leaking out about a quart not every ~80 miles (it seems to be getting worse since my last oil change, that's why I'm thinking housing gasket)! I believe I should definately be addressing it. My question is regarding two areas that I am going to be looking at: oil filter housing and rear main seal. My question is this: if the RMS was leaking, would it only do so under pressure, or always (overnight, etc). Same goes for the filter housing.

If it IS the filter housing, is it a bear to change the housing to engine mating gasket? If anyone has performed this job, please let me know your thoughts. Thanks.

Head gasket at the rear.

Yes, definitely head gasket. I had the same experience with my 88 300CE

Wouldn't this show up as oil in the coolant, or vise versa, as well?

Matt, it's possible that the valve stem seals are shot causing the engine to burn oil, rather than leaking all that oil. How many miles on the engine, and has the head ever been reconditioned?

My 300SEL leaks oil from the head gasket too, but it is up front by the number two cylinder

Just replaced my head gasket (2nd time..) with the same issue.

If the rear main seal was leaking, you will find oil on the transmission bell-housing under the torque converter.

You need to wipe the area down completely, then start the car and watch carefully using a mirror. It should be obvious if its coming from the valve cover or the head gasket.
Look for oil on the block.

On my m117, the valve stem seal job took it from a quart every 100 miles to a quart every 3,000 miles. Take a look at the spark plugs--black and greasy looking?

Good luck.

i went from a quart every 600 to a quart ever 3k on a 103 with 150k miles..

went from a quart every 350 to a quart every 1300 with a 103 that had over 200k miles.

each time i did not replace the valve stem seal closest to the firewall...just couldn't get the tool in there.... i had a cheap tool, however.