Question regarding Oil leaks while under pressure M103

[MattBelliveau]

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.