Typically the old VW's start leaking around the pump. It's no big deal if you can turn a few wrenchs to replace all the seals. The only other thing to replace is the lines if they are old. Then you can run B100 all the time (except below 20).
Bio has a higher cetane already. You don't have to add the extra boost. However during the winter I add the antigel and mix 50/50 BD/Dino.