E30 Zone

Just acquired a 1997 E39 523i with the M52B25 engine, with around 154,000 miles on the clock, and rather black looking engine oil with some slight 'mayonnaise' under the oil filler cap - so an engine oil & filter change is obviously required.

Engine otherwise starts easily and sounds good.

Is it advisable to use STP Engine flush to clean out some of the gunk, or is this a no-no on the M52 engine?

I don't like using those types of additives. I would recommend doing an oil and filter and use diesel oil, and change it in 1000 miles or so

No need, just use fully synthetic oil and change it more frequent, using the engine 'properly' will soon move some of the muck rather than tickling the throttle for a couple of miles per day and barely getting it up to temp

use a cheap oil drive around block and drain it then fill with oil and filter of choice