If I look up the Cookers on google, much current or recent-enough pr on the band still lists Harper as a member. I don't know the whole story (and maybe nobody outside the band does), but wasn't following closely enough to realize that he'd split.

Kenny Burrell “Live at the Five Spot Cafe–The Complete Recordings” Blue Note Japan SHM-SACD   500×500 70.8 KB   Didn’t get a chance to hear all of this before going off to PT, so I’m listening to it again!

Disc 1 

United Artists  GXC 3136  ( Japan 1976) - Milt Jackson "Bag's Opus" -  re. 1958 - Engineer: Tom Nola    

Fantastic news. Over Christmas, we were watching the Charlie Brown Christmas Tales DVD, which included music I never heard before. Great stuff indeed!