I replaced a failed Taco 006-B4 with timer in the basement with a Kolerflo RS 15/6 recirculating hotwater pump. The Kolerflo 3/4" threads do not seal properly under pressure with the brass females-to-sharkbite-to-copper joins.

I re-set with a stack of rubber washers in each brass female and still get leakage (Kolerflo threads are cheap plastic and don't screw down far in brass females).
Also, the hot water is discolored yellow and smells like machine oil! Is impeller in Kolerflo compromised and leaking lubricant? Or might washers be causing the funky oily stink?

Is Kolerflo with threads a useless piece of junk and should I go with a sweatable option? Spring for a $300-$400 Taco replacement?

Hoping for quick hot water again upstairs soon.
Any words of wisdom would be much appreciated.
Thanks in advance.

From what I'm seeing, that model pump has a cast iron housing and threads. ?? Did you PTFE(Teflon) tape the threads? Pipe dope?

Threads are plastic. I used Teflon tape, did not dope -- will dope seal plastic-to-brass under pressure?

I would try both tape and dope, or return the pump for another.