One of the surprises when I bought my 86 GL new almost a decade ago was the
lack of a specified service interval for several items.  I have noticed
discussion on this lst recently about the lack of a replacement interval for
coolant.  There seems to be consensus to do it (but less on what to do it
with).  Incidentally I decided to replace mine every three years, and use
the VW stuff, and have had only a few tiny leaks.  

But what about other items??  VW ( and Bentley) say the hypoid gear oil
doesn't need to be replaced. Good idea?? [I still have the now 9 year old
original.]   VW doesn't mention the fuel filter, but I have changed mine
about every 50,000 miles.  I also replaced spark plug wires, cap and rotor
at 80,000 (even though all tested OK on my ohm meter) and performance seemed
to improve; and shortened the 30,000 mile replacement interval on plugs and
air filters.  And I have replaced drive belts every three years---one broke
once on a trip and tore up the plastic flange connecting a waterline to the
block which almost ruined a vacation and created a lifelong paranoia.  

Has anyone seen modifications from VW on any of these since the original
intervals were set years ago??  Or developed their own sense of reasonable
preventative maintenance??

                                            John Foster