My Mytol was the water based solution from p89 of the Film Developing Cookbook.The 3 year life in absence of air has not been verified by others AFAIK.For Dimezone-S, 7.5 year some life was reported with anaerobic Xtol:
Your precipitate may be glycol-borate complex ,we will never know.I don't think esters are formed at the mixing temperatures you use:

For other PC developer PC-TEA when selecting development times for different films I have used a simple multiplier of Xtol time,is there any reason not to use this with one of the concentrates?