Is there a known glucosepane cross-link breaker?
Unfortunately at this time, there are no known glucosepane breakers which can feasibly be used in a living organism.  There is a small (very small) amount of research being done on the topic by Yale university in cooperation with the SENS foundation, but the focus is extremely early stage - nothing more than synthesis and detection of artifical glucosepane and precursors.

It is a rather frustrating situation, as there are very good arguments indicating glucosepane as an almost universal 'bad thing that should be fixed', and the molecule itself isn't particularly complicated.  It seems that this would be a low effort/high reward research area.