Thanks for the additional information.
I actually had several thoughts as to why your cat might be behaving this way. If he were overweight, then he might not be grooming himself (because he can't reach certain areas of his body); as a result, oils might build up which he couldn't remove with his tongue.
However, if he's a good body weight, then this seems less likely to be the problem.
1. It sounds as if he may have discomfort or pain , though, which might make it uncomfortable for him to groom himself since he's have to twist his neck/upper body to turn around to reach his body. Cats don't typically vocalize a lot but they might if they're uncomfortable.
If his discomfort is secondary to arthritis or joint issues, then the following may be helpful.
a Cosequin for Cats which is a joint supplement available at most local pet or grain stores or online.
b. Occasional use of anti-inflammatory drugs such as Onisor which is licensed for use in cats but can only be given for three days in a row.
There is a drug called Metacam but it is somewhat controversial in veterinary medicine, at least here in the States It's use has been associated with significant damage to the kidneys and should be used with great caution in older cats; the drug currently carries a label to that effect. However, there are some recent studies which indicate that at very low doses, this drug may be beneficial for cat with osteoarthritis.
c. Adequan which is basically a stronger supplement but is an injection and needs to be given by your vet.
d. Fish oil supplements such as Welactin which is liquid that can be drizzled on the food. Also available on the internet.
e. Pain medication such as Buprenex can be very useful and could be given everyday or only on the days that he needs it.
f. NuCat Senior which is a supplement and source of antioxidants to reduce oxidative damage to joints. Also available on the internet.
2 I've seen a few cats with systemic disease (such as Diabetes) have a greasy hair coat although it would take blood work to determine if there's an underlying endocrine or other problem. However, if he's not grooming himself, this is probably why his fur is getting greasy.
At the very least, I'd start him on fish oil and joint supplements since these may take several weeks to build up in his system and be effective.
I'd also use a warm washcloth to wipe his fur down every day to help remove some of the oils. I wouldn't use soap but just warm water.
There's also a long list of possible reasons why older cats excessively vocalize which range from Hypertension to Hyperthyroid Disease to aging changes to hearing issues. So, while it's possible that this behavior is related to discomfort, there could be quite a few other explanations as well.
I hope this helps. Deb