Normally white foam on the oil filler cap is because of condensation settling in the oil pan. IE, not driving the engine enough to boil out the impurities.

The oil trap/oil separator is seldom clogged. What needs replacing are the lines to/from the oil separator. If you remove the intake manifold, be prepared to replace a lot of vacuum lines. The small ones tend to crack with age, especially the 90 degree elbows.

Migrating oil to synthetic seldom causes seals to blow. Old original seals might leak because the sludge covers them and allows the seals to dry out. A small amount of weaping then happens until the seals swell back to their original size, usually by the second oil change.

I would check the compression every 6-12 months to ensure the gasket is OK.

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