Regarding the trimer of Glyoxal:

The trimer when dissolved to produce a weak solution will revert to the monomer within 24 hours (in darkness).. so claims a paper on the fixation of tissue samples. Unfortunately, it doesn't supply quantities, but does reference a another paper - Earl B. Whipple, "The Structure of Glyoxal in Water". So far I haven't been able to find a free copy of Whipple's paper - JACS wants $$ to read