Question for the structural/unibody experts
I purchased a used M4 last week from a BMW dealership, non-CPO. All is well so far. Considering it was bought from a BMW dealer, and a reputable one at that, I didn't bother to get a PPI because I thought I did my due dligence (carfax, excellent service history, and my own visual inspection). So shortly after I bought it I took it to a BMW specialty shop for a mechanical check and body check. They said it was great mechanically but could not vouch for it in terms of the body (accidents, etc). So I then went to a reputable body shop. They put it up on the lift and noted two things:
1 - Front bumper was painted at one point but they assured me it was a merely a respray and that there was no other damage associated to it. Overall, they said the body and frame looked great and basically guaranteed it was never hit.
2 - They did note something a bit odd though and I didn't think much of it becuase they assured me it was not a big deal. They noticed that the area behind the driver side rear strut was of a different coating/color than the passenger side behind the rear strut. See images. I asked them why that would be and they really weren't sure, but again, they said it wasn't a big deal. But they did spend some time comparing both sides.
My question is, are the circled areas considered the unibody? If so, is there any reason why it would be a different color/coating on both sides? Again, the body shop didn't seem concerned at all but also didn't have a reason for why that happened. Naturally, my curiosity is peaked and I'm thinking worst case scenario - previous lease owner had frame damage and had a piece of the frame welded hence the mismatch in color. I figured I would ask here to see if anything else noticed this or has this on their M3s/M4s?