Sorry you sound like you know a fair bit about hamsters anyway
It's difficult I know - I had a similar thing the other day - found a lump on our Robo. I thought it's unlikely they would operate on an older robo and wondered if I should just leave him to carry on. But - even though you think the vet can't do anything there may be something they know that we don't, or they may be able to prescribe something that helps. Or advise/diagnose/or just suggest things we hadn't thought of.
So I am taking our robo to the vet, because the vet knows more than I do and to be sure about things and discuss what next. So maybe a similar situation.
I don't mean to preach to the converted - but I would hold off cleaning anything at the moment -that could be partly why he got distressed - I know it was only a potty and the sand bath but maybe just do the potty next time and try not to change too much at once if he's feeling a bit vulnerable and unwell.
When they're poorly I don't think it's essential to have things perfect/clean. Within reason.