Marco the 535 is the RCD predesessor to the 555 and no longfer in production. As 2slow indicated it is not shift selectable and if it is marked JR or Airt it is positive shift not negative. he only thing you could try is factory service however I have doubts they will do it either.

Another alternative is to pull a trade with someone else with the wrong Rx, people buy the wrong ones all the time. That is the down side to internet shopping and places like Ebay.

John