I read some of the post again and I was just thinking about something that happened to me with a S series machine and I would guess that a late production date of a 763 may have had the same thing , under the seat , in what I call the cowl , there are two hidden holes that are covered with plastic plugs , under those plugs you can use an allen wrench to get to a bolt which acts as a adjustment -limiter , and I seen where the part the allen screw threads into breaks off and screws up the travel of the lever movement , I would doubt it could happen on both sides at the same time , but maybe if the machine was equipment with that and they were out of adjustment it could be an issue