Yes, I've broken a bolt too. I just built a MS310. Build started out with a MS290 Mahle cylinder, snapped a bolt, tried extracting no go. So went ahead and got an oem 310 P&C (I already have an 039 that I built).
For the 310 I did a preassembly run. On an empty cylinder, tapped holes with a twist tap bit, cutting lubed, just a little to allow bolts to engage. Cleaned out the the shreds. Set bottom end dry to act as bolt guides, used old seals for alignment. Used cutting lube on both bolts and in holes, flooded the holes. Did 1/4 turns. Once all were tapped through, disassembled and cleaned up everything again. Then assembled everything with sealant and P&C lube.
In hindsight I think the bolts are good for one tapping run.