synthetic vs. conventional & time to change?

[roccit_53 at scirocco.cs.uoguelph.ca (C Boyko)]

I figure oil is cheap insurance, so I use Mobil 1 in the Roccs or Delvac 1
for the TDI if I can get it, if not, the dealer Castrol, though the car is
much quieter on the Delvac. The Cabby gets whatever's on sale, so do the
Fords. I've never used synthetic in the Cabby, so who knows what new leaks
would sprout. I'm due for changes on the lot of them for winter storage,
but I'm waiting for Mobil 1 to be on sale. The Cabby has a jug sitting in
front of it, wonder when the garage cat will get that done, what good is
she anyway?
Cathy