@ipaul321 have a look in the back of the shifter and see what colour the cable bush (the part that the gear cable is fitted through) is - if it's black, contact us and we will send you a white one which is an easy retro-fit - some (not all) older stock has a cable bushing that is susceptible to damage from some mineral oil-based lubricants over time and this may be what is at the root of your problem. The white replacement bushings that are far more resistant to the mineral-oil based lubes that shop mechanics (and others) have a tendency to spray around with gay abandon.
We can't simply use a white bushing to repair the old lever as once the damage has started, a simple cable bushing replacement does not make for a reliable repair - there is other knock-on damage that quickly occurs after the damage to the bushing that means a new lever body is the best & most reliable fix.
For the record, these shifters are generally reliable if they are not subject to lubricants being sprayed into them - but a good many mechs and others do so for reasons that escape me ...