God, OP, that’s dreadful! My skin is crawling just reading that. Yes - once a certain point is reach, earlier things which you were able to see as innocuous suddenly look very different.
Have you decided on your approach yet?
Many years ago, there was a man in my church who did similar….. a handshake at the peace would linger just…. too…. long. He also had a really weird and disgusting way of raising an eyebrow while looking you up and down. There was more as well - things he said to, and about, women.
I spent many a sleepless hour going over in my mind what I was going to say to him. I came up with the perfect, calm formulation of words. Then when I went in the next time I knew he would be there, all prepared to say it, my adrenalin was so high I was practically hyperventilating and on the verge of a panic attack. So I said nothing, and resorted to physical avoidance (piece of furniture between).
He knew what I was doing, and on one occasion objected because someone else had had a kiss and he hadn’t. I didn’t respond.
So, I was a coward. He lost one victim, but was able to carry on with impunity with all the rest.
It is so, so hard to call this stuff out - especially when there are extenuating circumstances, like in my church, where everyone is supposed to be nice, or in your family, your poor widowed fil etc.
So, so hard. Take courage. You don’t have to allow him to paw at you. The thing is…. you asked how to ask him politely….. why is that? Is it because part of you thinks his behaviour is unintentional and he’d be mortified if he thought you were upset by it? Because the more you say, the less likely that seems to be the case.
There is still the dementia possibility, and someone has sent you some helpful resources on how to deal with that. But even if he is in the early stages of dementia, he should still be able to understand the word No.