I also tried some conditioner spray, which had some small effect so I got the idea that maybe, since he hasn't had one in 5 years, maybe he needs a bath with real shampoo & conditioner.
So yesterday. coming back from BayCon, it was a warm, summer-like day, and I figured he could dry off on the patio. So I gave him a bath.
Observation #1: There are some sounds a cat can make which they only make in the bath, and maybe just before death.
Observation #2: If you thought it was difficult giving a cat a bath, try giving a cat a bath with a thumb brace on.
Observation #3: It is much more intelligent to flip the shower/sprayer switch over to sprayer before the cat is in the bath and all soaped up.
Corollary to #3: You must be this tall to hold the cat down and reach for the switch atop the shower head
Observation #4: If the cat did not appreciate being shampooed, it is not necessarily true he will appreciate rinse, conditioner, rinse.
Observation #5: It is impossible to overestimate the amount of water which can be retained in the fur of a 20-lb. domestic long-haired cat.
Observation #6: Giving the cat a bath only makes the matting worse.
Constructive suggestions would be appreciated.