Replacing the Black back and front case on my son's iPhone 4s

My Problem

Used your excellent guides, but got to a point of no return.

My Fix

Came across two motherboard screws whose heads chewed up and lost any grip on them. It was decided that it was either a micro drill out to proceed or give up and a complete reassembly with the Liberation Kit and spare screws . Opted to reassemble taking it slowly and gently. No rush. (He has the previous models).

My Advice

Be very careful to engage the head of the screw with no force, because it is unlikely you will see the head damage until it is too late. Check: is it turning or chewing up?????