This is an incredibly reliable envelope feeder. 24 per minute, and nary a jam.
After many years of use however, the feed rollers became smooth and shiny. Cleaning no longer fixed the problem.
What to do? The only listed parts are an entire replacement envelope feeder for hundreds of dollars.
Then I found a site with detailed parts diagrams and parts lists. Aha! Looks like RBI-8063 and RBI-8064 are replacement roller sets that might solve the problem.
Next, www.copierpartsexpress.com has and/or can order all the obscure parts needed. At a discount. Less than $25 plus shipping and we had what we needed for the repair.
A friend took care of opening up the envelope feeder and replacing the parts. Took him half an hour or so.
One last trick to get past a very scary immediate result: the printer kept complaining about the envelope size! Turns out that the feeder has it's own "smarts," and got out of sync. We changed the envelope size setting on the printer front panel, changed it back again, and all was well.
Here are some other helpful resources found along the way: