unertl bv-20

i traded for a unertl BV-20 that has issues that i need to address. it is missing the 3 “rings” that go on the tube. the first being the lock ring that goes to the very front. next are the 2 rings that go between the spring. and last is the spring. i can make all of these. but; i need information about this particular scope. what end do i screw off to install the rings and spring. the front would be the easiest. ( if it does in fact unscrew ). the rear has more “stuff” to remove . the parallex adjustment is at the rear and is VERY hard to turn ( the lock ring is loose) if i can remove the  back, i would be able to maybe loosen the parallex ring. can't find any literature (instructions) for this particular scope. any help  would be most appreciated. especially information and instructions.