porky,
Are they the original screws/bolts?
If they are not, see if you can thread a fine-thread bolt in the threads (UNF 1/4" x 28).
If you are sure they are the original screws/bolts, do you have a tap and die set?
If you do, carefully clean the threads with a tap.
If you do not have taps, you might want to buy a cheap set (not for tapping; for cleaning/"chasing" the threads).
Or,
use Bubba's thread cleaning/chasing technique (view to the end - use a tap)
