No point in replacing the vapor barrier if it isn't torn. Just wasting time and money at that point.
It's a good idea to have extra butyl on hand, but I find that if you separate the vapor barrier by cutting the butyl with a knife as you peel, you can clean the butyl and "reactivate" it with some 3M adhesive cleaner. It actually makes the stuff incredibly sticky and seals great.
I got my car with 2 leaking vapor barriers, which made the car smell like a swamp. The 3M stuff got those stuck on good: http://www.zhpmafia.com/forums/showt...467#post580467
With the number of times I've replaced window regulators and door lock actuators in my E38 and both front regulators in the ZHP, I've never had a leak using that stuff.
'04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 111k
'98 740il | Schwartz 2 | Sandbeige | 5AT | 238k | lowered on Bilsteins w/ B&G springs
'00 540i sport | Titanium silver | Black | 5AT | 120k
'85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 215k | one owner, all original