Roadworthy gave you good advice. I would just add a minor nitpick that lead oxide is only going to exist at the battery terminals and I would think by now you have cleaned those. Far more likely is iron oxide (rust) at your ground cable connection to the frame. Steel wool and/or sandpaper (and bolt tightening) are good there. I do not know about the GR2110 but the BX2200 and similar (as well as many small Deere, etc.) have a widely reported issue of failure to get a good 12v to the solenoid to engage the starter and turn the motor for starting. Usually blamed on the long string of safety interlocks. If you get clicks and the motor will not turn over and you have a good condition battery AND you have cleaned all the cable connections (forget your sprays), then the infamous failure to get good voltage to the solenoid is probably your issue. My guess is that after you do what Roadworthy says it will start fine for quite a while. If the disease comes back a bit later I suggest a quick easy test: Hook a battery charger to the battery terminal no matter what the condition of the battery, even if the battery is the best in the county. The charger will put MORE than 12v on your cables to the solenoid and it will probably starter at the time of your next outage.
