I too have rebuilt/resealed many (maybe hundreds) of boxer engines over the past 23 years. I don't hear any talk about the head studs being stretched. The heads are held to the block with very little torque, and the hardware integrity is very important. Just compare a new stud with a previously used one, maybe on that has been torqued 2, 3, 4 or more times and it's obvious that they do stretch. Also, sealer on these head gaskets is very important, I use perm-a-tex ultra grey and have never had a problem. Ever. But be very careful not to use too much. This is not a case of lot is good, more is better and too much is just right, like my fathers view on horsepower. On the top of the block I use the same ultra grey. Be absolutely certain to clean, clean, clean the sealing surfaces, use alcohol base cleaner or something that won't leave a residue.

I'm sure this has been bounced around plenty, so forgive me for the broken record... That's my 2 cents on the leking head gasket talk that seams to haunt the list.
Jeff Hogue
84 Westy
87 Syncro Doka
8? Iltis Diesel
03 Jetta TDi Wagon
90 son
94 daughter
62 wife.....