Without actually seeing the slide "in person" it's not really possible to determine if the pitting can be polished out by a pro re-finisher.
ANY pitting can be polished out so long as it doesn't go so far in that polishing would weaken the metal.
The problem is, if it's too deep, the slide markings will be blurred or removed.
Great restorers like Doug Turnbull can not only polish out the pitting, they can also restore the markings in many cases.
Price-wise, this may or may not cost more than a new slide.
Another factor is, can you find a replacement slide with the same markings?
Colt markings change fairly often, and some of the older style marked slides are almost impossible to find in new condition.
If the marking don't matter, you could simply send the gun in to Colt to have a new slide properly fitted, or buy a replacement from Gun Parts Corporation or another parts supplier.
