iamdub
Full Access Member
The Castech logo can't be seen unless you remove the rocker pedestal rail. Regardless, if the oil didn't have the telltale yellow/cream/milkshake stuff or black and sludgy (from the moisture being steamed out of it but other coolant chemicals remaining), then your coolant and oil aren't mixing. You have to be sure of what you're looking at, though. Ask your dad to clarify if coolant was, in fact, in the oil.
Castech or not, it could be a head or block with a defect and crack. Or a failed head gasket. Maybe the owner prior to your mom somehow ran it hot and warped the head slightly or the head gasket failed and it was such a small enough breach that the stop leak was able to patch it. GM has their own "stop leak" tablets for the cooling system that they've designated as a viable repair. As far as rebuilding at only 162K, I don't see why it'd need that if the oil didn't have water in it and if the oil pressure is good/stable. I've replaced Castech heads on a 182K-mile 5.3 that was so sludged up from coolant mixing that it clogged the pickup tube and lost oil pressure. It was brother's truck and it came to me with collapsed and clacking lifters. Surely had bearing wear, but no scoring. Thoroughly cleaned it out, slapped some used 799s on it as I received them from a FB Marketplace find, replaced the usuals with the only upgrade being a high volume oil pump (with stock pressure relief spring) and sent it. Almost 5 years and 50K miles later, it's still towing a trailer with 4-door RZR, dirt bikes and 4-wheelers to his camp three hours away and back.
If yours is or was just slowly burning off the coolant through a combustion chamber, then the engine's bearings and rings should be in great shape with another 160K+ miles left in it if it hasn't been beat on. I'd have the heads checked for cracks and cleaned (including a cleaning pass to resurface them) with new valve seals and lap in the valves. While they're off, closely inspect the block for cracks. Pay extra close attention to the head gasket when you disassemble it for evidence of failure and patching from the stop leak.
Or, as @rockola1971 and @wjburken suggested, if it ain't broke, don't fix it. The RMS job doesn't really have any connection with a head job. You can R/R the heads with the engine in the truck if you need to dive into that down the road. It's kind of a "do everything or just do what it needs" thing that you'd have to determine based on your resources and other goals (all new gaskets, if you're dead-set on cracking it open for the coolant thing along with the RMS job, etc.).
