oil retention valve

[Lyle]

I know a couple of audi engines use these.  Not sure about the 5-cyl engines
but the 6 and 8 definitely, one in each head.  I guess they're supposed to
keep oil up in the valve train after the engine shuts off, and I gather that
they are known to fail after 130,000 miles or so.  I'm going to be pulling
my intake manifold soon, and figured I might just replace these "while I'm
in there" due to the high mileage.  Is there any way to test them to see if
they are failing?  My shop manual doesn't say.