airbound I think

First time post, please help.  Boiler issues, almost 1300 dollars in repairs and plumbing bills.  Cast iron boiler that needed a new expansion tank as the high pressure valve kept releasing.  Air was definitely introduced during the replacement process and likely had been introduced due to the old expansion tank going (it was old and might have been diaphragm-less).  There is no heat in 4 of the 7 main floor radiant baseboard heaters.  It is a cast iron boiler with an auto air vent and only one zone with shutoffs to isolate the circulator and one drain inside the boiler.  There are manual vents on all of the main floor vents and a couple of accessible vents in the ceiling of the basement (there could be hidden ones as almost all of the ceiling in the basement is finished.  The auto valve spits out a sparse amount of air occasionally and I have gotten very little air out of the manual vents upstairs and most of that is cold clear water, water out of the high pressure valve is blackish.  I did get some air out of one of the vents upstairs by lifting and rattling the line a bit and then it ran black for a time with some warmish water but now it is cold.  I have bled all of the vents I can find and I have tried purging the system by connecting a hose to the drain in the boiler and letting city water course into the system both at partial pressure and full and I got some bubbling that way but I didn't let it run to clear as the bubbling was sporadic and I was told not to put too much water in.  Sorry about the long post but I am at a loss with what to do.  I was pumping away but the plumber told me that it needed to pump towards so that got switched.  He won't fix the issue now or rather he says he is all booked up which means the same to me given his usual availability.  I can get pics if need be, please help.