I would just take the switch box apart and fix it for good. If you haven't done this, it's a piece of cake but it takes a while. I've done it several times and here are some pointers I've learned.
Open the switch box inside a 1gal Ziploc (there are 10-20 tiny ball bearings and 4-6 small springs inside and opening outside if you aren't prepared they will spring out all over the place).
The switches work on roller/rocker/spring operations.
The points under the rockers get corroded (clean with steel wool).
When you put it back together, I've found the easiest way to ensure that all the bearings/ springs and rocker points to stay in place is to use small dabs of dielectric grease on the rocker pivot points, ball bearings and springs.
I've rebuilt/ cleaned 4-5 of these and never had this not work.
Or, a sledge would work too