Sealing mirror gasket

[blown motor]

A previous owner had installed a passenger side mirror that was from some other vehicle. He had puched a couple 'non-factory' holes to do this. I am now installing the correct mirror and will drill two holes to put the screw inserts into. I'm thinking  I should try to seal beneath the gasket to prevent water fron getting inside the door via the old holes. The new gasket will cover everything. Should I lay a little silcone on the backside of the gasket, put some around the holes from the inside after the mirror is installed or is it not necessary?

[burdar]

Just put some paint around the edges of the holes so it isn't bare metal.  You don't need anything else.  Water is going to get down into the doors no matter what.  It will run down between the window fuzzies and the glass.  That's why there are drain holes in the bottom of the doors.  Just make sure those drains are clear.