I just bought a used 1998 Legacy 2.2 5spd MT with ~169,000 miles on it. I'm looking for replacement knock and downstream O2 sensors for it.

 

For the O2 Sensor, I am looking at the Bosch 15726. Is this a good sensor or should I go with the more expensive OEM part?

 

For the knock sensor, I have not yet found a suitable part. Are there any non-OE parts or should I stick with OEM?

These vehicles like OEM parts.

I have used eBay Knock Sensors (from China), for less than $15 incl. shipping.

They work just fine; the only problem is that they take a few weeks to arrive.

They're so cheap, that I ordered a spare to keep on hand (but I've never needed it).

 

If I remember correctly, I was quoted over $100 by a Subaru dealer for the OEM Subaru part.

EBay and amazon knock sensors are fine. They work well and last just as long as the more expensive ones.

+1 to ebay knock sensors.  they're cheap and i've never had a problem.  get two or one of those and one used one - or save your old one if it's still good and yo'ure replacing pre-emptively?  1998 knock sensors are definitely on ebay.

Bosch is ok for the O2. They have been the OEM supplier at one time or another.

 

Denso and NTK are ok also.

 

O.