Sometime in the late 70's to early 80's GM changed the dip stick tube. Instead of an O ring seal it used a rubber sleeve. The case hole is the same so the later tube will fit any case. You can order all 3 pieces new from a GM dealer or hit a wrecking yard to find a set. Be sure to get the stick with the tube so your readings are correct. To install slide the sleeve into the case then put some oil on the tube and slide it into the sleeve and attach the bolt to hold it in.
Sounds like a truck dip stick and tube. The locking cap was brought about in the80's to prevent fires if the tranny vent became plugged. So instead of blowing out the dipstick tube onto hot exhaust it blew out seals.Phillip my th350 tube and dipstick has the rubber sleeve seal but the tube is too long and indicator has a locking feature and it hits the hood insulation. The aftermarket chrome don't fit on firewall clearance and have the o-ring. Would you happen to know the part numbers from GM that properly fits the 69 Nova?
The salvage yards just have bent up junk so far?? Thanks,