i see that there is glue and pads.whats the best .i can detach base with little screw.i assume its best to glue base first ,then attach mirror once its solid to window?

Mark mirror post on the front side of windshield so you know where to put it. You should be able to see the impression (glue) where it was. Clean area on the inside, read instructions included in glue package.

Any experience with pads vs glue?

The mirrors were originally attached with the pads. I've had good luck with reattaching the mirror as originally done, but by using two adhesive pads instead of one. Later cars use the adhesive that seems to work well, and I've used that on my '84 911 with good success., so I imagine weather should do the job for you.

I've tried on 5-6 occasions to glue mirrors on before I tried using the pads. I'll never use glue again.

I think there is a difference (albeit small) in the curvature of the windshield and the mounting surface of the rear view mirror base, hence the compress able could sided adhesive pad. The two pad trick was given me by an old parts manager at the local Porsche dealership.

The later mirrors (on the later 911s) have a much smaller, probably slightly curved attachment, so the glue works fine on the 'button' type rear view mirror.

Let's say that a rearview mirror fell off of an old 911 and was glued back in place a little too high, how would you get it back off?

Heat the base with a heat gun, and pray a lot. Cracking the windshield is an expensive way to remount your mirror.

So with the use of two pads,one goes on mirror base one on window,then attach to each other?is best to glue base without mirror until it's solidly attached?