Most problems I see with M70 safeties are caused by people trying to force the bolt open with the safety on.
With the safety on (full rear position only), the safety plunger (part 23) locks the bolt closed by protruding into the cocking handle about 1/8". Trying to force the bolt open burrs the end of the safety plunger. Then the burred up end makes the safety sloppy loose, or difficult to apply or remove because the plunger can't slide back and forth in it's hole.
Take the bolt out of your rifle and try the safety. If the safety still acts the same, it's all in the bolt sleeve and safety parts.
Check Youtube for Model 70 bolt dis-assembly (compress the spring and slide #15 off the firing pin). Remove the firing pin and spring, then the breech bolt sleeve (part 25) with the safety in it. It's easy, but they won't go into how to take the safety apart. The safety is simple, it's only 4 parts. Most people file a finishing nail to a flat point to tap the little roll pin out.
1) Tap roll pin 26 into the center of the bolt. Place it somewhere you won't lose it!
2) Now you can wiggle the safety lever (part 21) out of the top of the bolt sleeve. Be careful, the safety plunger (part 23) and spring (part 24) are going to pop to the back. Some people do this inside a plastic bag so they can't lose the little parts.
3) If 23 and 24 don't pop out, use your little finishing nail and tap them out towards the safety lever hole (the rear) of the bolt sleeve.
4) Most likely your safety plunger (23) is burred up, or rusty, etc. Clean it up until it slides freely in it's hole.
5) Put it all back together and be happy.