Dunno without looking at it. Something worn down or worked too deep is my guess, but I'm not all that familiar with M70 safeties. I'd have to take mine apart.....
Mine, bought 2nd hand, but in almost pristine condition, had an inoperable safety also, from the factory. I put in a Tubbs system, but didn't really need to , as I could have worked the factory striker instead. I went with the Tubbs to hopefully improve the accuracy, but it did not.
If you need said striker to fix yours, pm me. I don't need the factory original, with less than 50 rounds on it, I believe.
Oh, yeah- if you are putting that striker spring etc back together, be sure to close the garage bay door first. There is one part in there that has a range of over 50 feet....