Most bilge pumps are easy to fix. External float switches, simple wiring and easily cleaned contacts make it so. However, the RM2000 is different. It would appear to have a solid state sensor. I don't therefore see that it will be an intuitive repair.
The only thing I can add, after reading the brochure on these pumps, is that if they detect oil (which can occasionally be found in bilges) they will not function automatically. Perhaps this may be the problem. Alternatively, the sensor may be fouled with debris.
Of course, the problem with highly intelligent bilge pumps such as the RM2000 is that they can be more intelligent than people like me...and that can be a separate problem which is generally irreparable.
The good news is that 2000 GPH automatic bilge pumps can be bought new for not a lot of money, and the reasonable news is that you could rig an independent float switch to the wires from the RM
2000 to the panel; but this might cause the manual overide to lose its function.
Given the overall importance of the whole let's-not-sink-the-blasted-boat concept, a new RM2000 might be a reasonable investment.
I wish I could be of more assistance.
"if at first you don't succeed....Redefine success"!