Firstly, good luck with your challenge.
However.
If it was put in a basement, it might be because the fault you can see had happened and the owner didn't know what to do (or similar).
The basement treatment may have done further damage but it might not be too bad, depends on a number of factors.
Critters using it as a toilet is a common basement activity.
My Hammond A100 housed a few generation of mice without permanent damage.
Also the Rhodes got mildew on the vinyl and speaker cloth, but nothing worse.
Cleaning the pins and sockets on the chips is a good place to start, psu
also.
If the front panel switches actually have a hard fault, a few locked on instead of off would confuse the processor.
You could unplug the bendy wheel assembly, that's quite complex on the OB8, but it might need a shorting link to bypass it properly.
Connectors the next place to go.
In the older models, the white Molex connectors were the usual problem in this department, but I recall they changed those on the OB8.
It's hard to measure the ribbons reliably, sometimes they get intermittent.
They might be ok, they don't usually need to be treated in solvent, maybe a careful recompression of the idc-ness.
Replacements aren't going to be off-the shelf, like a Mackie
I
would disconnect the ribbons and remove the main pcb, examine it with a
watchmakers magnifier or similar, looking for breaks, corrosion etc.
Then brush it clean with a small clean dry brush.
If
there are spills of beer or soft drinks spill onto the pcb, sometimes
careful removal with appropriate solvents will wake it up.
In more modern stuff you can't usually get under the ICs nowadays to really get it clean, a proper ultrasonic bath treatment is required.
I wouldn't recommend re-capping any more than I would tell you what shirt to wear for a date.
Plenty of people will of course.
You can only tell if caps are faulty if you see leakage, blow-outs, broken wires or if you can infer that from a circuit malfunction.
Re-capping could be starting a fight you might have trouble finishing.
I would say the original OB8 construction is first rate and unless you feel totally confident that you can do work up to that standard you may cause premature death rather than revival.
I would have confidently claimed that 30 years ago, but looking back, there's nothing like factory conditions for a first class construction.
None of my workshops was ever that pristine.
While the construction of the OB8 isn't microscopic, it's small enough to need
excellent viewing conditions for any pcb work.
If the thing wakes up at all, check the keybed still works, they don't like basements, but they're not too hard to clean if the rubber pads are still in one piece.
The OB8 is less modular than the previous big Obies and needs more understanding to break in without knowledge.
This combined with the above warnings might make you rethink.
The symptoms you describe may well remind somebody of a previous problem and cure they got.
That is kind of like "My Uncle had spots like that and it was an allergy".
