That's the first thing I'm going to fix. I'll pick up one of the better penetrating oils that have been suggested on the thread tonight.
My machine has three sets of feed roller assemblies, so we can still use it in the field, then work on the one busted assembly during down time.
If The stuck screws still won't budge with muscle power or with tapping, I'll pick up an impact driver to tackle it.
Thanks for the advice.
Re: Suggestions regarding the application of heat which you have reasonably rejected. Try dry ice which can be purchased from many supermarkets. The difference in the coefficients of thermal expansion or contraction is the operative force. You may recall that Indians split rocks by drilling holes and filling the holes with water soaked fibers which upon freezing expanded fractured the rock. Granted the fact that water expands upon freezing but the principle is the same.