As I start putting my project car back together I am concerned about bolt torque.

There are several conditions that exist when tightening a bolt:

1) New bolt going into a newly tapped hole

2) A new bolt going into an old hole with minor effects of age

3) An old bolt going into an old hole, both with the effects of age (in my case the car is 41years old).

Take for instance the M12x1.5x30 bolt that attaches the caliper to the carrier plate. Lots of rust. The hole has been cleaned by running a tap through it, then flushing the hole. The bolt (for the most part NLA) is in fairly good shape. A new bolt would be used if found, but the PET and the shop manual don't give a clue as to the specs for the bolt. I could assume its a 10.9 fine thread but is that all I need to know? So take this an example case.

I'm pretty certain the the specs in the factory manual are for condition 1 above. When putting these back together we're at condition 3 above. There is significant resistance when threading the bolt into the hole. This will give a false torque reading and possibly result in under tightening the assembly.

One could lube the threads with oil to reduce this friction. On a new assembly, oiling the threads reduces the required torque by about 20%. Ignoring this can result in over tightening the bolt resulting in possible damage to the assembly.

So, what does one do when faced with conditions 2 or 3 above? In this case I cannot get a new carrier plate so my best case is condition 2.

Any ideas?