Hi MMV, didn't want your post to go unanswered. My Dad has alzheimers, in the early stages his symptoms were similar to those you describe. seven years down the line and his symptoms are quite severe. Not saying this is what your dad has, but there are drugs which can help people with alzheimers, slowing the process down a bit, they have helped my dad. Also in this country until you have a formal diagnosis, you can't access all the help you may need.
Also my mum has had a lot of help from social services, doctors and support groups etc. - from practical things to help my dad - memory aids, exercises etc, to help with sorting out finances, taking charge of his medical decisons, and many others things.
The head in the sand approach doesn't work, as you obviously feel also. Its hard for some relatives to face what may be happening, but if your dad had a broken leg or something he'd get medical help. Its sad when people ignore a mental decline, because there is some help available.
Just to repeat, I'm not saying your dad has this it could be any number of things, but ignoring it won't make it go away, and there could be things that will slow the process down for him if he does have some for of dementia. You could try phoning one of the charities for alzheimers and ask for advice, I think ignoring symptoms is quite a common phenomenon so they might have some suggestions.
Hope every thing goes well, its not a nice thing to face, but having said all that, although my dad's illness is quite advanced now, his eccentric sense of humour has somehow survived, and despite the illness, I can still see my darling old dad in there somewhere. Good luck with your situation.