Hi,
So I know the AO-101 is not the hot topic anymore, but, I have one and have some general questions.
The RAMBO board is labeled 10000282. The printer was made as one of the last before the TAZ was released.
Would the latest versions of the Marlin software run on it?
Does this RAMBO board have inputs that could be used for bed leveling?
Does it make sense to just upgrade to a new Arduino MEGA and a RAMPS board?
And, I suppose this should be separated into a post in mechanical…but, assuming I got both the bed out of level and the Z axis (left and right) out of horizontal, what the best approach to getting things back again. 
Regards,
Mac
Yes, the latest version of marlin would run, and it would require extensive customization. It would be easier to also convert it to 24v and a hexagon hotend at the same time, then you could use the Taz 5 firmware as a baseline with the ao 101 z steps value.
You could enable auto leveling, Taz style or probe style, they use the z endstop plug plus in the case of a probe, voltage.
If the board is working, it’s fine as is. Rambo 1.2 is the newest, and newer than ramps.
To get back in level, measure from the bottom of the z axis bearing blocks to the motor mount and adjust both sides to match, then heat to temperature and move nozzle to each corner, adjust the z height until the lowest corner is about 1 business card thickness away from nozzle, move to the next and adjust until all 4 corners match, then print the calibration pattern, then a cube, etc.