I just bought a 1 owner 300d that has had oil changes every 5k and valve maint. every 15k. I searched the archives and got opinions on timing chain replacement. The car has 197k and I want to have the chain replaced. How much can I look to spend? Also the a/c needs recharged due to leaks. The mech. that has serviced the car since 22k said there is a GM kit for $600 that converts it to R134 and replaces all the seals. Has anyone heard of this? I have not.