My suburban has 250k miles on it and I'm finding about a quart of coolant vanishing every couple months. Oil change didn't reveal anything in there and I don't see any leaks on the driveway. I'd like to avoid waiting until it dies so considering a proactive rebuild. Any opinions on having this motor lightly rebuilt (head gaskets, bearings, and rings) vs getting a used 5.3 and swapping that in instead? Good rebuilders in California? Maybe just keep driving till it dies?