Glad you got the problem licked. This is one of the few instances I recall of a manual transmission having a serious problem develop, among items posted here.
Is this a 6 speed manual transmission? If so, maybe that partly explains it. According to one report I read, Porsche’s 6 speed manual transmission on the Boxster seemed to be more problematic than their 5 speed. Maybe stuffing 6 speeds in the same size case requires some compromises.