I had my vacuum modulator valve replaced a month ago and a couple of weeks later my reverse started slipping to were it is now no reverse. All other forward gears are fine , shifting is good , the shop wants to rebuild it to the tune of $1,500.+ , can I adjust it to work or do they just take a dump without warning like this? Could it be the valve they replaced? The car only has about 160,000 miles I'm the second owner, and the orig. owner took excellent care of it.Any thing I'm over looking or ? Thanks to any and all help. C.W.