I have a question regarding what maintenance I should be doing on an older water softener.

I just purchased the home last spring. The previous owner installed the softener in 1986, and has done nothing to it but add salt for all these years.

I have the initial water test done by the installer - 17gpg hardness, trace Iron (essentially, none.)

It is an Erie Manufacturing Co. softener, and the tag on the control head on the resin tank identifies it as a Model FAS-22. It has a mechanical clock and cogs to set the regen interval.
The resin tank is fibregalss, roughly 36 inches tal in total (including the plastic "stand" , but not including the control head).
The salt tank is 32" tall by roughly 15" in diameter.

My concern is this - the previous owner filled the salt tank with road salt ocassionally. Every spring, if he had a couple of bags of salt left over from the driveway, he'd use it up in the softener.

I can see dirty layers of salt near the bottom of the tank.and it looks like a layer of silt/dirt/general crap in the bottom of the tank, under where I assume the salt screen should be. I can also see a brine water line on the tank, roughly a foot up from the bottom, that goes down during regeneration.

For the first few months, the softener seemed to be functioning properly. I was adding 88 pounds of proper softener salt every 2 months to the tank. However - this month, I noticed on the calendar it was time to buy salt. When I checked the tank, it hadn't used any salt since I added it 2 months ago...

I pulled the long tube out of the salt tank and cleaned it up a bit, water flows freely both ways...I did a manual regeneration, and it seems to be working again... but for how long...

I took a water sample in for testing, and the raw water is still the same as it was in '86 - 17 gpm hardness, no iron. The "soft" water tested at 5 gpm hardness.

Any thoughts or advice would be appreciated. Thanks!