603 oil use -- cause?

[Jeremy5848]

Our new-to-us 603 (135000 miles, unknown PO history but probably not good) uses a little oil -- enough so that you can see a little haze from the tailpipe upon acceleration. It isn't a diesel haze -- it smells like oil. The engine has no noticeable leaks.

The engine has gone about 1000 miles since the last oil change (Chevron Delo 400 15W-40) and is down about half a quart, maybe a little more. My indy mechanic opines that, on this engine, the cause is more likely valve guides rather than rings. Even so, this is an expensive job on this engine and, as he says, "you can buy a lot of oil for a thousand dollars."

I had thought to acquire the necessary gauge and, while I have things apart installing Brian's EGR testing kit and cleaning the crud out of the intake, to do a compression test. I had read somewhere here that compression should be checked with the engine warm -- is this correct?

Anything else I should check? I don't mind adding a little oil here and there, just want to feel better that the engine is not gonna fry itself some day soon. The car starts easily -- for a 1987 603 -- and runs well. I'd like to be able to keep it.

Jeremy