Been away for a bit, sorry for the lack of response.
o.k. - I can lift the subvalve to disengage the teeth from the rod, and the rod will still not move at all. The rod must be removed before you can remove the subvalve, so both of them are stuck in there (for now). The subvalve will freely rotate if pulled up and disengaged from the rod. Engaging the subvalve to try to drive the rod out is no help because I can't put much torque at all on the subvalve. So, I'm putting the main shaft in, engaging the rod teeth and rotating the main shaft to try to pull the rod out from the front.
I tried a vinegar soak for a couple of days, no help. Need to get more penetration into the rod bore to get at the corrosion. The cylinder is currently at a bike shop where they are trying a combo of heat and penetrating oil, the idea being that the aluminum will expand more than the steel rod and let the penetrant in. Find out tomorrow if it works.
I also spoke with Jeff Fredette about this problem. He said he has seen one like this before and was able to fix it, and also has some good used jugs in case it won't fix. So, all in all I'm in good shape going forward.
I asked about the source of the problem (water/coolant), he said most likely a head gasket leak but that he was just guessing. When I get to that point I no doubt will be looking for ways/tips to ensure a good gasket seal to keep this from happening. Regular KIPS maintainance probably would, anyway.
Thanks for your questions & comments, I''ll let you know what happens.