Tach drive bolts are 2BA, first try, use a small centre punch , make a small dimple near the perimeter, then try to drive the screw round to unscrew, this works most of the time. next try, if that fails , punch the dead centre and drill through with an 1/8 th drill, left hand drill if you can get one, then take a small torx bit and drive it into the hole, then unscrew.

As well as the spindle there are other sealing details, an O ring for the drive spindle, gasket , tab washer, and where the tach drive cable screws on another O ring to seal the cable. the cable should have a flat wire reinforcement and heat shroud at the lower end.