We repaired them by fitting an "o" ring in the groove, sliding in the seal end of a sleeve, cut off to just above the machined surface, then building the groove up with "Molecular Metal". When this hardened, remove the cut down sleeve and "O" ring and you have a perfect seal groove.
This repair lasts for many years, I have been repairing Major blocks like this since the 1960's.
The later Super Majors had a second "O" ring at the top of the liner and the problems were reduced, but after 50 plus years you must expect a few problems.
This problem is not really the same as the later porosity problem which is due, in part, to the short stroke, "knocky" engine in the '000nd series.
There were some casting quality problems too. We had tractors with "hard spots" in the bores when new, which honing would not remove. These appeared after around 300 hours. We were fitting sleeves into new tractors to cure it.
There is a fine article on this problem from Cat. who also suffered from it in some models. It is on the internet but I do not have a link to it. It is well worth the read.