I would do a good cleaning now if possible, get all the gunk off his penis and out of the sheath. Greasy gunk holds germs well. I would not advise using mineral oil, the KY jelly, both are greasy and stuff sticks to them, you can't rinse them out or off the sheath area. Horse is just as dirty with stuff stuck on him, within a couple days of using those items. Needs cleaning again.
Can you use someone else's Excaliber bottle, pay something for the cost of what you use?
Dial soap is always recommended for sensitive area cleaning, wounds, just not sure how well it cuts grease to get the gunk out. I know people use lots of liquid dish soaps, but then you hear complaints about how horse reacted to such strong chemicals after. Could be they don't rinse him well, or he is sensitive to the stuff in those soaps.
Again, using the warm water, rinse him REALLY WELL, get everything out of his sheath area. We run a hose from inside the house outside to get warm water for the cleanings.
Do look for more than one bean, I have often found several small ones on the same horse during a cleaning.
I thought the Vet was out, to be prescribing meds you named. Yeah, money is tight, but sounds like horse needs attention now, not "eventually". Part of the cost of owning them is care when they need it. I would be quite worried about the fluid buildup, nothing normal there.