I think I could build that if I had a good drill press.,

Yep.I'd drill & tap & run a bolt in it, build a "tail stock" for the bottom end , fake up a "tool stand" & get some tool steel & shape it up to hold an O-ring, Yea, gimme a late 60's Craftsman 3/4 horse drill press with the T'Bolt plate & I could do that. FWIW, for practicality's sake, time required to build up the setup I could probably get a machinist to do it on his lunch break for $20.00 & a 12 pack,, & Id be ahead. But, in a pinch, I do believe I could make that happen.,.,

Update to a long idle thread.

1st prototype using standard o-ring material initially sealed well and lasted about 10 months before it started leaking.

Since the original design wasn't made to my specifications I was limited to using only 1 o-ring.  And because that did work w/out issue till the o-ring let go, I'm revising the design to be a single o-ring.

I have hi-temp O-rings on order and will replace it with the new design over x-mas.

One concern I have, And I'm sure if it has any impact.  Having had several had several of these plugs in my hands and seeing the wear patterns they caused on the cover... when loose these things rattle.  As I'm replacing a rubber over steel plug with one of entirely aluminum... I'm afraid of precisely fitting the plug between the cover and head.  I'm thinking of undersizing the head and providing a spring or another o-ring to keep the plug seated and prevent extra wear on the critical o-ring.

Whatta you guys think?

Probably could be done.
If you could tighten it from below with a flex drive, would solve a lot of issues.  But over tightening could cause failure.  Loosening from vibes or thermal cycling.  Having to apply locktite (heat sensitive).  Or simply the same issue of burnt rubber.
but, if tightened from above, would limit it to having to remove the cover to get access.  Why bother.

I'm hoping the new O-rings will solve the longevity issue, and in working out your idea, I think I solved mine.

I would think using just 1 O-ring would allow the plug to vibrate pivoting around that O-ring.  Might try a slightly longer plug with 2 or 3 O-rings to stabilize the vibrations as well as seal.  If I had to guess, that's why Suzuki's entire plug was covered in rubber.

I'm not an engineer; I'm just a volunteer in a soup kitchen serving food for thought.

ZAR, you got mail.

How bout posting the specs on that plug so someone with a mill/lathe could fashion up a few?
The wife's started leaking last month, I've tightened the nuts fore and aft but it is still seeping, so plug change is in order.
I live near a few military bases and lots of gearheads in the shop I used to work in was an aircraft engine shop.