One of my books says 1987. But that may be the last point at which the author saw them for sale. Opening the possibility that production ended a bit earlier. It would be interesting to hear from owners what the date stamps on their ones are.
I can't imagine why anyone would have bought one once the HW77 came out. On the other hand, stuff like the Webley sidelevers soldiered on into the late 90s: you could still buy a "new" (maybe slightly old stock?) Tracker in March 2000.