I was hoping somebody would replay to this. I'm in a similar situation. I bought a 210c that has a "broken" transmission. I think the reverser is bad, but the sump and pickup were missing. I found a new sump and pickup, but the pickup won't be here until next Wednesday. Have you dropped the sump and looked at the screen yet? I'm an auto mechanic, so not a lot of experience with hydraulic systems. I have been studying the manuals for the 210c, and I thought the reverser had its own 8 qt supply of fluid. I wasn't sure if it ties in with the rest of the hydraulics.
You may want to drop a note into the Hydraulics forum on this as well. Most of the guys that know hydraulics are familiar with the various types of pump systems too.
If it looks like you gained oil but did not, you have an air leak in a return line.