We have been using the same set of plates that originally came with our 377
sequencer which we obtained nearly 5 years ago. I haven't seen any problem
with plates that isn't cured by a dishwasher wash with no soap used at all.
For us the majic trick has been very hot distilled water washes. Are you
sure there is no dishwasher service at your location that you can utilize?
We have a facility that does dishwashing for us and we simply request that
no soap be added. Works miracles.
Good luck