My suggestion is to break your VHS audio into reels, then use audio from another source to bridge any gaps between reels. Reel changes are where frames typically get dropped.

The reel changes are listed somewhere around here, but I remember Reel 1 ends at the transition to 3PO's oil bath, Reel 2 ends after Tarkin says "one swift stroke" (well, in English!), Reel 3 ends (I think) after the Falcon is captured, just before Tarkin says "Yes" to his intercom. And there's one right in the middle of the compactor scene, just before Luke comes back out of the water. My memory is pretty fuzzy beyond that.