When I ran a stock block, I checked leak down a few times per season, and I have a system one oil filter, so trash in the screen and percentage of leak determined when it was time to rebuild. That usually worked out to around 300 passes. Since I switched to an aftermarket block, I tore it down after 4 seasons and it looked like brand new, so I am back to filter inspection and cylinder leakage. I also have a valve spring tester that fits the rocker arms, so I check springs when I adjust the valves. The aftermarket block was the best investment I ever made. Its a world products aluminum block. I do the transmission every third season. 3200lb car, runs 9.70's