Pulled carpet to see how rusty it was today 1980 300d. Pretty cool to find the seat belt anchors on both seats not attached to any thing but carpet. Not sure what to do next. Mike

Not attached to floor???

Yep. Rusted off the frame. I think I figured it out. The seat belt reel has a bolt nearby. I bought some longer bolts. (Surprise. Not metric). Used a cut off wheel to remove the rusty nut an piece of body work . So my anchor is holding the belt reel and the other end of the belt. Genius. Plus the belt was flipped tangled in the reel and now it reels up. Yay for me! I’ve been driving this for at least 10 years with the belt only attached to the carpet!

But now the load is doubled on that one bolt. Feel safer? It should slow you down a bit, maybe, before it breaks off Can you install a plate to cover the rusted area, from the underside so it catches something good? Put your bolt through that. Tack weld, bolt or screw plate to underside. The underside will be doing the holding.

Thx insidious. I will cobble some floor patches in the near future.