Yeah, the OP can't win, heck can't even break even on this.
getting FIL to repair/replace the unit....he loses, as if FIL will do that...(a real man would offer though)
asking FIL to repair/replace the unit..he loses as wife will be 'bent out of shape' ( how dare you ask ! )
paying for it himself, ..he loses, out a LOT of coins (grr, I didn't cause the problem...)
not repairing it..he loses , the USE of his machine (grr, I didn't do it but have to LOOK at it...)
If FIL won't pay for the damages, park next to garage,best spot, in front of wife's car. When asked when will it get fixed....show the estimate from the dealer to her and say when 'we' have $xxx, THAT'S when it'll get fixed.