Originally Posted by greisinb

... 4) Get a vise grip and lock on to the brass casing. It will start to spin while tapping and you will want something to prevent that. ...

Originally Posted by mln01

Thank you for spelling Vise Grip correctly! There are far, far too many mentions of vice grips on this forum. Vice grips would be a whole 'nuther thing!

Originally Posted by greisinb

Thanks @COSitsWORTHit for the suggestion, it worked well! Here's how I did it if anyone is looking in the future.
1) Source a fitting with a 1/8 npt (National Pipe Thread) thread, my fitting was a 1/8 npt thread to a 1/4" tube which works with the tube already in the truck (even though it's metric). If your breather tube is broken you may want to consider a 90 degree fitting. Mine was intact so I used an inline fitting.
2) Source a 1/8-27 npt tap and tap wrench (you can get them off the shelf at NAPA).
3) The tap technically requires a 21/64" hole but the position of the brass casing makes actually drilling out the casing difficult because there is no clearance for a drill. Luckily the brass casing is close enough to the required size and can be tapped without drilling.
4) Get a vise grip and lock on to the brass casing. It will start to spin while tapping and you will want something to prevent that.
5) I put grease on the tap to catch as much of the swarf as possible and started to tap the casing. This was the most awkward thread job I've ever had to do because not only are you upside down but you have to put quite a bit of pressure on the tap because the casing hole is a hair too small. I had to try several times before I got a good "bite" on the tap and the actual threading started.
6) After the casing is tapped apply Teflon tape or pipe dope to the fitting threads and thread the fitting in to the tapped casing. I had to remove the vise grip but was able to put a suitable amount of torque on the fitting.
7) Push in the breather tube and you're all d