Thank youuuiu 🙏

https://uk.subaruownersclub.com/forums/topic/2366-manually-reading-ecu-codes/ has clear codes process in the post.

I managed to find an o2 locally, fitted sweet and plug matched, $100, looks like it come from aliexpress originally haha. arrived today. Installed it and took it for a drive. No check engine light, but the codes still showing when checking ecu memory, I’ve forgotten how to clear codes on the obd1 system. So I can clear codes and take it for a long drive to see if anything pops up. I’ve  got green plugs and clear plugs under the steering wheel. clear plugs together shows the codes through the flashing check engine light, green plugs together doing nothing. Am I forgetting something? 

When I got my BBS wheels they came with 225/45-17 Goodyear F1's - an absolutely awful tyre, in a totally wrong size for a GC8. Rub-dub-dub and raised the overall gearing enough to take the edge off performance. Switched to 215/45 tyres - much better response and grip. 215/40-17 was even better, lowered the gearing enough to make the car feel like it had an RA

Hmmm, I have inherited a 1999 SRX, could totally replace the o2 with no real repercussions.. tempting.