LDM... Don't open the holes. That can induce flutter and trim issues. I just mentioned it as one source of why servo's chatter. OK, if they are really tight, you can very slightly enlarge the hole, but you don't want any slop whatsoever. In general, I'd think you'd never need to enlarge the holes.

There are ways to reduce the linkage friction at the connections. Best way I know of is ball bearing linkages, but they are expensive and the diff isn't significant enough for typical sport use to justify the cost. FYI... I have several planes with ball bearing linkages. Very friction free setup... When I turn off the radio, all surfaces instantly droop. I still have servo chatter. The surfaces move so freely that the weight of the surface and even air movement in the room do to central air is enough to get the servos to bark almost nonstop. This is normal.

Cheers