Reading my Bentley manual, it says to toss the seat floor mount bolts and install new bolts only if you take them out. Why? Do they stretch?

BTW, what are the thread sizes and bolt length if I can find some grade 8 cap blots to replace the old ones? Or, do I have to order them from MINI?

 

You should get the correct ones from MINI. They will be the right hardness and of course the right thread and length.
"Grade 8" as you referred to, is a hardness rating for standard thread bolts. The MINI is all metric. The numbers on the top of a metric bolt is the hardness.

 

Bentley says that about everything. Just reuse them.

 

I agree.

 

I reused them on a car I retrofitted the heated seats into, but the rationale for tossing them out and using new bolts is the factory applied threadlocker.

The bolts have a small patch of threadlocking compound "printed" onto the threads of the bolt.

Rawhyde

 

I had to remove the rear seat track bolts when installing my German-sourced armrest assembly. Just reapplied new Loctite threadlocker. I can't see a reason to dispose of them as they're not torqued terribly tight nor subjected to extreme temperatures.