My Bach valves started hanging after about 6 years of use. I too was using Al Cass. I got a new set of valve springs, cleaned the valves and casing with acetone (watch out if your horn is laquered!) and switched to a synthetic oil La Tromba T2. No more problems.
If I look at the wear pattern of the valves where I only used Al Cass, I see sub optimal protection. I don't use it any more and have become an advocate of synthetic oils. They just seem to hold up better.