Modern Vespa

Just did a valve adjustment for the first time on this scooter, 2006 GTS 250, with 20,929 miles. Results are that the intakes were right at spec, 0.10 mm. The exhaust were so tight, I could not get a 0.10mm gauge in. Adjusted to 0.15mm.

However, I did notice some corrosion on the case face and suspect that the gasket was starting to fail? Although i did not see much deterioration in it. See pic of corrosion.

It doesn't look like corrosion. When aluminum corrodes it turns white. That looks like some kind of gasket sealer. You have to remove all of it but don't scratch the metal.

True, a typical aluminum oxide corrosion is white. But put dirty oil on it for a few months....

If it was mine I'd make sure it was smooth and button it back up.
Could have been a slightly loose screw. Or a gap in the gasket, but if there's no weeping, more likely just an unlucky spot of corrosion.
Riding in the rain, or being a bit *too* meticulous about cleaning could both result in such corrosion. Far, far more important that the exhaust valves are now properly adjusted.

How easy/difficult did you find doing this job? Did you do it with the engine in situ or did you drop the engine?

That looks like polymerized oil to me. There shouldn't be any sealant on that surface.

^^^^
This. Oil was smeared there at one time (very easy to do) and has then 'cooked off'.

You'd soon know if there was a leaking cover gasket - there'd be oil all down the face of the head.

Lowered engine since I am doing a shock replacement, rear brake caliper replacement, so rear tire was off, I loosend any hoses wiring etc and jacked it up to drop the engine. This gave me clearance to work

The remedy is easy enough — gently scrape off the polymerized oil with something that is either not very sharp or very very sharp. I would start with a credit card or other piece of stiff plastic, and then maybe try a piece of 3m Scotch Brite, but GENTLY. If that didn't work, I would resort to a fresh utility razor blade, but at a very shallow angle. Otherwise, you're liable to nick the aluminum.

I use a length of 3/8 copper pipe, with the end hammered flat and then sharpened with a file. It's great for scraping off head gasket debris and other stuck on shit from aluminum. Soft enough it won't hurt the aluminum, sharp and strong enough to remove nearly all unwanted cruft.

watch this for a video on it.

If it were iron, I'd call it well-seasoned.