Betor Forks were some of the best available back in the 70's.
Oil leak from fork cap
Oil to Use:
Use 230 ml of 20 or 30 weight Fork oil per fork leg.
(Non-Fork oil will foam up)
Oil coming out vent holes:
Cut out a plastic disk the diameter of the springs, that wedges in the spring, so that oil squirting from the damping rod doesn't hit the bottom of the fork cap
Rebuilding involves dissasembling the forks, checking for damage, replacing seals and o-rings and then reassembling. Check out this link showing the process. (go)
Honda CL 72 (25) and CL77 (305) seals are sized: 35 x 47 x 10.6
(Honda PN: 91255-273-000)
Sliders worn out
Worn sliders can be rebuilt by boring and inserting a bushing. Follow this link to learn more (go)
Definitely replace your old sacked-out springs. AMS & Speed & Sport can both give you new springs. The springs I got were too long and I had to shorten them. The 1974 Pursang 125 were shortened to 42cm (16.5"). Use a grinder to flaten the end of your cut so that it doesn't gouge the fork cap.