[Vwdiesel] Replacing flywheel bolts

[Libbybapa at wmconnect.com]

I am currently putting a 1.6TD into an '83 diesel vanagon.  Before putting 
the engine in I am changing basically all of the seals and gaskets (except 
head).  Looking at the vanagon Bentley, they say regarding the bolts that hold the 
flywheel to the crank "always replace, insert with D6 locking compound".  As 
they are not stretch bolts what is the necessity for replacement?  What is D6?  
Medium or high strength?  Do others typically replace those bolts?  Can I 
just clean them meticulously and reuse?
Should be the same for any other IDI diesel VW.
Andrew