For those that use F1s and have got them trough mytyres, there is a guy on the BM boards that had one fail when he was pushing on in his M5. Rumours are that there are some japanese F1s knocking about that aren't E-marked and are not up to scratch quality-wise.
Might be worth you checking. Mine both say made in germany and have an E13 marking on them.
Just thought I'd pass this on.