After being parked since the fall, my TH350 transmission was low on ATF. Wouldn't back up, dipstick was dry. I found silicone sealant around the speedometer drive gear. Apparently the PO had issues before I got the truck. Just wondering if a gear from a TH400 would fit, just happen to have one of those. I am not concerned about speedometer accuracy too much. The truck is a 1986 C10.