[DannoXYZ]

You mean nuts? I think they're 8x1.25mm. Can get replacements anywhere. Better yet, some self-locking copper ones:

And some star-lockwashers.

And torque wrench

 

[DannoXYZ]

Those studs look way longer than they should be. I'll have to look at mine. Maybe they were replaced by whatever someone had available.

Looks like header was repaired and/or O2-sensor flange. So very likely replaced with whatever handy.

Mine are 20mm long. Just enough to hold sensor and nut. Hate having to thread nut all way down extra threads

 

[DannoXYZ]

Well they came loose today and now my exhaust is somewhat loud again.

What did you do to repair?

Just pushed O2-sensor back on and installed nuts?

To what torque did you tighten those nuts?

 

[DannoXYZ]

I use air ratchet. All those extra 5-seconds adds up!!! :grin:

 

[DannoXYZ]

So after your co-worker pointed out your O2-sensor was loose, you:

1. Left it loose?
2. Drove home and O2-sensor fell out rest of way and dragged on ground?

What would cleaning inside of exhaust do?

Yes, you need new O2-sensor, a manual and torque wrench. Only do procedures prescribed in manual. Follow it manual precisely. When it gives torque number, make sure you achieve that number.

 

[DannoXYZ]

Hoping next shop does what you pointed out.

Shops will only do what you tell them. Otherwise they will come up with huge list of "must do" items and charge you tonnes and problem will still be there. YOU must be chieftain of your cars' maintenance. Otherwise i hope you are independently wealthy and can afford to support team of mechanics... and their wives and kids... and their McMansion and country-club dues... :grin:

 

[DannoXYZ]

It should be better than the other place, that welded the flex pipe and must have stuck it back in with no bolts ? Because the revving loosened it, and it isn't supposed to...

You should go back to flex-pipe place and demand they cover cost of new O2-sensor. Or give you all money back for job poorly done. Hopefully you put this on credit-card so you can easily dispute and get refund. No excuse for such shoddy work.