I have a 93 Buick Roadmaster that is our daily driver. It has about 92K miles on it, and I've been using Pennzoil HM 5w30 with a Napa Gold filter and 3000-3500 mile OCIs. Is this a good choice, or being that this is an older engine is there a better option? I've considered going with a synthetic, but I've heard that it's not a good idea to switch an older engine as gaskets and seals may start leaking.