It's a bugger when they leak oil.The design is good,the grommet compression is all that is needed to pull in the covers to mate with the sealing surface,if all is flat and true.The landing on the bolts is measured as a stop for any more (excess)grommet compression.You could machine these back a little.A finer thread into aluminium(aluminum),the cheese of all metals would be a design error resulting in the need for a thread insert.You may be stuck with needing a new cover.Refacing,you could try wet n dry sandpaper on a mirror or "flat glass".good luck.