since OP has the dust caps (or at least one) my 2¢ is
clean the threads with alcohol and apply a drop or 2 of LocTite (Blue or Purple) and maybe you'll always have those caps!

IMO only downside to the Nervar Star is the uncommon BCD(s) the early Gen used 122 bcd and later Gen used 128 bcd (which DOES allow use of some Stronglight rings, maybe some other FR brands that made a variety like TA?)