W124 seatbelt rail removal

[j-galap]

Hi folks,

I just took the passenger seat out of my recently acquired 1995 E320 wagon:



As you can see, it ain't pretty! Planning on taking the carpet out entirely to clean up and potentially get dry cleaned too.

My question, though: the seatbelt rail (bottom left). The 10mm bolt on there I began to undo but it for some reason starts to feel tighter after a few turns of the ratchet which is slightly unnerving. Before I go any further and potentially screw something up, is there something I'm missing the other side of the transmission tunnel? Doesn't seem like it would be engineered to that degree to me, but this is MB so I thought I'd check!

Can someone shed some light on the situation?

Also, while I'm here, any thoughts on getting rust stains out of carpet?!

Cheers