I had the same thing happen to me last summer, bought a used Velvet Drive and worked fine the rest of the summer. About a month ago reverse went on this transmission. Rebuilt old trans and other than the lock rings it wasn't too difficult - the thread on TT about how to rebuild it is EXCELLENT. Seems to me all that needs to be replaced is the reverse clutch/clutches which is easy.
Check your model number, mine ends with -001 which means 1 bronze reverse clutch, model number ending in -004 means there are 2 bronze clutches and 1 steel.
Taking transmission out is kind of a pain though, get a $20 bottle jack from auto parts store to tilt engine and put a tarp over carpet/gunwales or you'll get trans fluid everywhere; at least I did the first time.