Thank you for enlarging the pics. Navigation got so bad last night I loaded three new browsers to try out. After I posted it wouldn't even refresh, I thought that post failed too (which would have been a fourth fail of a long post...Aaarg!) The posts will get shorter as we learn how much you already know.
I'd clean the eunit as CW suggests. The motor looks good overall, 'cept the pilot wheels (small front) have a gunk ridge on the treads to be cleaned
(Fyi, Photos are great for seeing stuff the naked eye misses. Every tiny flaw seems to be highlighted. Drives modelers nuts )