Is the switch getting HOT? If so, the clutch could be starting to go bad. As the coil on the clutch starts to go bad, the resistance (ohms) in it start to go down (ie...it starts to short out). This causes the current-draw (amps) going thru the clutch to increase. This will eventually burn out the switch and blow the fuse. I had the switch on my Turf-Tiger melt down before the fuse blew.
I am thinking that the clutch may be starting to go, so the resistance is getting low in the clutch coil, causing more current to be drawn and overheating your switch. Just a possibility.