What makes you think that the stringer is gone?
Reason I ask is that we thought we had the same issue, but it turned out that the holes for the lag bolts simply had enlarged and wouldn't hold the lag bolts. What I did was:
-- remove the bolts from the engine mounts, one at a time
-- cut a bunch of wooden toothpicks (preferably those thicker round ones) in half
-- gather enough toothpicks together to just fit into the hole in the mount and slather them with caulk (I used silicone and don't wanna get into a discussion of just what caulk YOU may like!
)
-- stuff the half sized bundle into the hole and push them down
-- go do something else for a half hour or so, or do the other mount
-- squeeze some caulk into the hole (do NOT use an adhesive caulk or epoxy)
-- insert the lag bolt and tighten most of the way, let set for another half hour, tighten up later today or tomorrow; I let the caulk that squeezed up out of the hole on onto the lag bolt head in place to keep the bolt from unscrewing itself
Depending on how bad your holes are, and how deep, you may have use full length toothpicks.
If your stringers are really GONE, you'll have to lift the engine and do major surgery.
What engine do you have?
