Not sure that is red rot - loos like damaged lacquer, but waiting for someone more experienced to chime in....
Terry Stryker
Mirafone 186C, 186BBb, 184C, 186C clone
Gebr. Alexander New 163C, Vintage 163C, Vintage 163BBb
Amati 481C
Lyon & Healy 6/4
Kane Stealth tuba
A plethora of others....
The lack of nickel-silver trim on this one and lack of kranz makes me think it is a "186-S" student model. I owned one (5v CC), still really nice horns.
I saw this. A great deal for someone as a second, small CC or as a first CC. Excellent price. 186 leadpipes are readily available, yes? You’d still be way under fair value having some work done on this tuba, imo.