I hooked up an older Kenmore water softener with a new bypass valve.
Where the valve goes into the softener, it leaks. New orings when installed.
What do I try to fix this?
If you didn't buy the O-rings specifically for this softener, this possibly is the reason it may be leaking. If not, check to see if the assembly isn't twisted by the pipe arrangement.
Plastic is notorious for cracking so there's a good chance that bypass has a crack in it, causing the problem.
Read what the end of this sentence means.