Using an Air Compressor type bleeders, I assume one of the bug sprayers you pump up?
I have the Motive Brake pressure bleeder system. Bought it 10 or more years ago to use on my 85 Mercedes. It comes with the screw on Cap and section of hose to connect to the Motive.
Also came with the universal flat plate for MC types like my 86 F250, one of the old cast Iron rusty ones. Trouble with it, never could get tightened down to not leak and make a mess.
I up graded the 86 like your 89 to the aluminum with clear plastic reservoir.
I was at Hot August Nights in Reno (the big Hot Rod show) and bought a cap/hose for a Ford.
Trouble is, wont lock down on the reservoir. made for a later newer type.
Picked up 6 at PNP a while back, and dang if none fit. The 3 little lock tangs are longer. few day ago was there and grabbed 3 more and they all fit...Yeah. need to drill hole and add Barb fitting or...??
Simple to use the system, but this is getting to be a PITR.
What did you use for your MC?
Good to hear you found the issue with your starting. Simple fix, but difficult to find.
Goat