The screws that come with the Schallers are quite a bit shorter than the stock MM screws. But often the Schallers are just a wee bit too small to fit the MM screw heads in there. If you've got the short screws, try using something longer that fits (take a walk through your local Home Depot, etc.)
If you need to fill/re-drill the hole, toothpicks/wood glue are definitely good in a pinch. Better is a small dowel that fits the hole though- more wood. I've done this the odd time, works like a charm. When it's dry, re-drill for the screw and you should be good to go.
OK, do what I did with my JP6. Flush mount your Dunlop straplocks. It only requires drilling a giant 3/8" hole an inch or so deep in the instrument so that the straplock fits down in the instrument horn and is flush. Then put the screw in. This will solve all your problems. The screw will have new wood to bite into and the crack you made will probably get removed when you drill out the giant hole.
i think replacing the schaller screw with a longer more "aggressive" one is a good option.
if the threads in the wood are gone there is virgin territory further on up the road
MrM
ps: if my memory isnt completely shot i think billy sheehan had a column in bass player. and in the very same number they did the eb factory tour i read that he used heavy wood screws (you know those with hexagon heads that you have to use a wrench on) to bolt his strap firmly on..