USA 1991 240 SE, B230F engine. 158K miles.

Problem: oil leaking from engine during driving, primarily (only?) through the oil filler cap on top of engine. Not a lot of oil, but enough to coat the top of the engine with a thin layer after a 10-mile drive.

Diagnostics & repairs so far: first tried the simple approach of replacing the $6 oil filler cap. No change. After reading a ton about the flame trap system at brickboard.com and matthewsvolvosite.com, I replaced the flame trap and the short hose connecting the flame trap to the oil separator box. The flame trap was COMPLETELY clogged, so that was definitely a problem. After replacing with a new kit (from IPD), I'm still getting oil leaks at the oil filler cap. There's no apparent vacuum at the small nipple on the new flame trap (as determined by running the engine at pulling the vacuum hose at that nipple and testing for suction), and there's no real suction at the oil filler hole either that I can tell.

So, I suspect that the oil separator box is clogged up too. Is this a fair diagnosis?

Assuming so, I understand that removing the box can be a bit tricky ... but it appears that if I remove the intake manifold, access to the box would be rather straightforward. Is that a recommended technique, or is there a simpler way to approach it?

Thanks to all who have previously advised against non-OEM replacement boxes and making sure the drain tube underneath the box is not disturbed.

TIA.