Is my thinking correct? (Rainsoft Silver unit)

First thank you to the experts who volunteer here. I've tried to read everything before posting.

I have a Rainsoft Silver (installed outside in 1999, brass valve, mech timer) on which the timer motor has failed (again). I've ordered a replacement to buy some time.

In the end am I correct in assuming 1) the motors/shear pin/cams/valves will eventually fail, 2) since it's obsolete, Rainsoft will offer a new valve head/controller which I pay for, and 3) the chlorine in my city water means the resin will be due for replacement soon (how will I know)?

If so I'm just going to nurse this along until failure then buy a more reasonable softener. I'd just like an expert to check my math, thanks!