You don't have a healer?
If you did, you could try a double reduction team on Tech Master. Put Gravitron as a leader and try to find a Flame Drall as a helper. I believe the Drall has an orb switcher for more heals. Then if you had a healer, you could put her in the group and use her skill. Plus the bump in RCV would help.
Is master much better chance than expert? (Well at least twice better?)
I have a ton of healers. 4 dryads, 1 5 star fire healer and 1 5 star siren.
Maybe next time someone in has a 50 percent green defense up, I'll try master.
My main concern is the boss healing, how often does it heal? If its only once then I should be OK but if it does it multiple time then I'm effed.
If not I can also load my team up with RCV characters and just let my nukers slowly take it down.