Wow. Lots of questions
I have 161K on my '97 Zetec, timing belt was changed 2 times, at 75K and at 150K, both pure maintenance,both belts we removed looked like new.
1st time (like your case) we didn't remove the valve cover and didn't know about the pre-tensioner spring and we changed the belt only (no tensioner/idlers). WP shaft was slighly rattling, replaced with an autozone one.
So it looks like the $7 spring is not an absolute necessity if you don't forget to tighten the tensioner.
2nd time I bought the Gates kit, replaced the belt & tensioner, left the pulleys alone (I was unable to remove them, and they still looked OK so I abandoned the project).
As for the other questions, I haven't heard about Zetec oil pump problems yet, and WP problems are also uncommon (but not unheard of) AFAIK. I can't really recall a single post about oil seal problems, remember quite a few 'timing belt snapped' posts though.
Tiv
