Fur clump on dwarf ham, please advise!

[lycrael]

I noticed while handling one of my dwarf hamsters, Millegan, that he had a patch of fur that was clumped a bit, like when you get something sticky in human hair. I took him out of the cage to provide a dust bath, but as always he simply dug and did not make any effort to roll or groom his back. I decided to give him a sniff after I couldn't make progress by taking sandy fingers and gently stroking the area, and I believe that it is urine. A a few days ago he got into a spat during an introduction to another dwarf hamster, Booth, and Booth urinated while flipping/running and I saw a few drops had gotten on Mill's forehead. As Millegan is young and has always been clean, I think that the matting may be urine that I did not wipe away after separating them. (I have heard that hams who smell of urine may also have diabetes, but given the matted area and the incident with Booth I think the smell is coming from that spot specifically). I know that you are generally advised to never wet-groom a dwarf hamster, but as it is urine I am worried about his skin. He seems completely befuddled by sand and has not addressed the patch of fur in the days since the incident. Is it, then, wise to rub that small spot with a wet substance? A brief Google search turned up grape seed oil mixed with water as a possibility, but it did not address urine specifically. Any suggestions on how I should proceed?

Update: I threw out his nest and noticed that ammonia smell, too, which might have contributed to the smell or could be the origin of the patch if he rolled on a wet spot? That's all conjecture but I took out everything I had let sit between cleanings (I didn't want to tear up the nest because of a recent cage change, but I also should have paid more attention to its cleanliness! D: ). Do you think this will encourage him to groom that spot/give him less he needs to clean so he can focus on that patch? I'll be away for the weekend so if it isn't an emergency (I'll keep an eye on this thread before leaving and during the trip in case one of you guys reveal a serious problem) so he may get a chance to work out the spot himself...

Apologies, new rodent owner and still not used to what's normal for them. Thanks for your guys' time to look this over!