by Dean Aukes
On the tan foamy sludge, I've had that in varying amounts on the oil filler cap of my '73 type 4 engine camper for the last 9 years. With the thermostat and flaps fully functional, I would get a little of it; without the flaps and thermostat working properly (current engine), I get it on the cap and some in the filler tube.
As I understand it, it is due to the oil never getting warm enough (>180F) to get all the condensation out of the oil. It isn't immediately fatal, but doesn't help your engine in the long run.
There have been many discussions over the years on the cooling flaps and thermostats. Bob Hoover has a few sermons on it and is very adamant that they should be in place. I tend to agree with him in all respects though my practice has been a little more lax. VW wouldn't spend money on something that didn't really need to be there. I think it makes a difference on the long term life of your engine, say 60,000 miles vs 100,000-150,000 miles that Bob gets. On the flip side, there have been posts of engines making 100,000 without flaps, or testimonials of folks whose flap linkage caused overheating and they would never use it again.
It's up to you. There's lots of stuff in the archives on it. I'm basically a stock kinda guy, so I would tend to agree with the VW factory and Bob.