I've done a bit more reading on this.  Seems a few others have had adherence problems with the Alclad primer, and the issue seems to be the type of plastic!  On some it is bullet-proof, on others (like my Fouga apparently) it adheres poorly.   I'm not that keen to strip it all off and start again, so will sand and patch the spots where it lifts, this time using decanted Tamiya spraycan primer through my airbrush, and hope for the best.   I hope other sections of paint don't j