I don't know about any "guidelines" from Winnebago, but I have had my Cummins w/Allison tranny (Spartan chassis) serviced at Cummins locations, Western Diesel, Truck Fleet, and mobile service guys. I would also have it serviced at Flying J "J Service" location or Speedco locations. If I had a CAT (and I presume you have a Freightliner chassis?), I would look for any Cat or Freightliner service places ...most truck service places could probably handle it.
A good place to check out service locations around the country is
www.rvservicereviews.com
__________________
Paul (KE5LXU) ...was fulltimin', now parttimin'
2022 Coachmen Leprechaun 319MB
towing 2017 Jeep Grand Cherokee Limited