I recently posted on the thread about Diff Housing Carrier Bolts some info gleaned from Jim Berry the semi retired (He's 75) Brisbane Competition Clutch Guru what he has found recently with Chinese crap creeping into aftermarket and now some Manufacturer supply lines, What I forgot to mention in that post I Have now edited it even Clutch Diaphragm Springs have become suspect even from Name suppliers.

He has tested said items for some of his long time customers at seasons end and in some cases earlier when problems arose only to find it seems Chinese spring steel is making inroads and in some cases after just six months the tension has dropped to lower than a stock diaphragm spring, That may be your problem

Most important Clutch Information in that post gleaned from one of Australia's best Clutch People Jim Berry