Hello Mary! I can't believe Percy is an older ham now
. Does he seem ok in himself? When do you go on holiday? If he seems ok in himself, then if it is something serious there isn't much they would do at his age apart from keep him comfortable and give metacam so it's a tricky one.
It'll be upheaval for him going to your friend's house but he'll settle there. One thing I'd suggest is having a phone call or two with him
If your friend doesn't mind. I vowed to do that if I ever left a hamster with someone again - just so they hear your voice. We left Charlie somewhere for 10 days and that is a long time for a hamster - I think he'd adapted to never seeing us again and was quite stressed on his return. After that I've either had a petsitter coming to the house (worked well) or taken the hamster with us (holiday let). But if I did leave them at someone's house again I would arrange for a phone call or two - a familiar voice to reassure them.
As to whether to go to the vets. It's up to you really. If he is well in himself then it would probably be fine to wait till you get back. If there is time it could be an idea to take him and get some metacam. But if he's not showing signs of pain or discomfort he'd probably be fine without it.
I think you will worry if you don't take him to the vets before you go away. Timing wise though he'll probably need a few days to settle after the vet visit before he goes to your friend's house. So if timing is tight I'd wait till you get back - if he seems fine in himself or it's extra stress and upheaval.
Just read back and you say he's acting fine! He doesn't sound in pain. So I would wait till you get back. He could have caught it on something. If it was something like skin cancer there isn't much you can do. And you would know if it started to bother him.
One thought - have you checked his nails? They can get overgrown as they get older - he could be scratching it maybe? Do you have a photo of the scab?