Re: filling holes
Get some 1/2" dowel. Cut a piece about 1/2" shorter than the depth of the hole and epoxy it in the hole with about 1/4" countersink at each end. Then fill the 1/4" with a good epoxy filler.
For new holes I use a gadget called a Portalign to keep my 1/2" drill exactly perpendicular to the transom surface.
