Don,
I would (and have) changed all that out at the same time. Use a genuine
German made pump, NOT an Italian reproduction. I use the orange anti-freeze.
Use a genuine VW thermostat. I have heard too many problems with aftermarket
units. I would NOT put in a colder one. I WOULD think about taking the
radiator out and having it professionally blasted out. I would NOT flush the
system. The two times I did it made it run hotter. I think all the junk
ended up in the radiator.
Ken Lewis
http://neksiwel.20m.com/