Replaced old generator at rear of cam cover due to worn/damaged dogs on spindle. Was original unit !46k plus miles total. Verified that all was clean, installed "new" one obtained from a well known Jaguar parts supplier, although housing looked like a re-build. New unit fit fine,cam dogs lined up, o-rings set,etc.
Unit lasted apx. 1,000 miles over a 2 year period, then when parking car for winter, rear cover of unit ( which is press fit into housing) popped off onto floor. Circular scratch marks visible inside cover as if tach gen shaft drifted back. Tach did not read all the time either during life, came and went. Possible connectivity problem. Bad quality or fell apart/loosened ?