Yes its definately a corrosion pinhole. I stuck an awl in it so that's why it looks perfectly round. I found a second pinhole and it's right at the start of the fitting threads. (you can barely see it in the image).
I wouldn't be surprised if more holes are forming.
I'm sure I could plug these two holes with a tapered pin of some kind then seal the outside with JB Weld. The inside bottom edge of the tank really needs to be sealed but I don't trust any sealants inside the tank. It might be worth the risk if replacement tanks were no longer avail. but I'd rather get a new one and not have to worry about it.
The entire rollover guard had to be removed to get the tank out and it's a PIA. The bottom 2 ROPS bolts are 24mm and must have been torqued to 300 ft lbs and had locktite on them. It had to dial my impact gun to max. torque to break them loose.