Hydraulic belt changer arms on 4020 HT

I was having an issue where when trying to switch into the low range speeds (40 to 2500) that the machine would sit there and click it's air valve a lot and would say 'waiting for air valve...' on the pendant over and over until it timed out.

This happened for a couple days, when finally it happened enough that it was stopping my programs so I had to do something about it. I inspected the air valves on the back of the machine. These were in good shape. So next I took off the sheet metal that covers the head / spindle to root around. I found that there was very little (about 10% full) hydraulic oil in the little black boxes that supply hydraulic fluid (via air pressure) to change the belts. It is unclear to me whether this is only on the high torque machines or not - anyhow I also found that someone had stripped out one of the aluminum metal that holds the two air -> hydraulic black boxes onto the hydraulic fluid reservoir. Luckily I was able the change the washer out for a thinner one and get some grip back on it. I refilled the reservoir and ran the range change a bunch of times until I didn't see air in the lines.

She's workin like a champ now. The low range belt also doesn't make squealing noises like it was prior to my oil refill. I noticed that the belts are cracked though and it must be time to swap those out when possible. I also noticed that I have the 'A' rubber motor mounts which are the long strips of rubber below the big metal motor mounts. I've read that there are solid aluminum 'B' ones available. My spindle motor jumps around a little when you fire it up when on the low range belt. Is that normal? Surely the rubber allows this to happen. In high range it doesn't happen. The shudder is worse now that the belt tensioner is pushing strong on the belt (because of the renewed hydraulic pressure).

Anyone seen this before? Am I headed for spindle trouble?

I have the 4020 HT model which is grease packed and compressed air cooled (no oiler)