I agree. Surprisingly little disassembly is needed to get these machines running.
Good cleaning in place, oil, new needle and thread.
I do not clean the tension assembly until I know how it sews. Once it sews, then I'll clean the tension.
My typical experience has been that the last time someone sewed on a 35# beastie, it sewed, and decently. A little bit of tlc and they sew like the champs they are.