2004 sprinter transmission does not shift. blown brake fuse!!

Hi i have a 2004 3500 with 148k on it and the transmission shifter does not shift from park to drive or reverse. I checked the fuses and the rear brake fuse was blown, also effecting my rear brake lights. I'll replace the fuse and everything will be ok for 2-3 days and then it blows the fuse.
Has anyone had this issue before? My mechanic told me it was the shifter shorting it out! $500 part to fix!
Help!!

It is possible that the shifter is the problem, but more likely to be a wire to the rear lights that is intermittently shorting out. Once the fuse blows you cannot shift out of park because the transmission does not get a signal from the brake light switch. The Sprinter has a history of issues with the wiring harness. Well worth doing some inspection before you part with $500.

ok, have you had any luck with this??? same troubles....

Jeff