Hey guys,
Just thought I'd share my success with installing a magnetic drain plug into my 6MT gearbox.
The plug i used is a Dimple M18 x 1.5 x 12 intended for a Harley, BMW or Mini.
Thanks for a chap on a 350Z forum who identified the correct thread to look for, sourcing a suitable plug was very easy and involved no trial and error (aside from the risk of the forum member stating the wrong thread spec).
The gearbox does have some magnets installed in the bottom of the box but those require gearbox disassembly to inspect and i doubt their strength. I found fine metal particles attached to the tip of the input speed sensor at the upper rear end of the gearbox (Aussie 370z's have SRM standard) and this caused problems with SRM. Although the amount of debris was negligible, it was sufficient to cause issues.
Total cost: AU$40 + shipping.
Comes with 2 aluminium crush washers. The plug is not compatible with OEM washers as the butt diameter is too narrow to seal properly using OEM washers (OEM washer has a larger inner diameter).
As you can see from the pic, the tip of the replacement plug actually doesnt reach as far as the OEM plug so there's no risk of collision with any internals.
New plug requires a 17mm socket to loosen/tighten. I've done it up to the FSM torque spec and will check regularly for leaks.