Any magnesium wheel gurus in here?

[MD427]

I'm having a fit getting some tires on a set of old magnesium Halibrands (I think *EDIT* 7.5" front 9.5" rear).

I brought them to a local shop to put 4 new tires on (BF Goodrich Radial T/A - same tire and size as what was on previously).

He puts the new tires on, and tells me when I picked them up, "its strange, the wheels/tires aren't meant for tubes, but the tires all had tubes in them."

I shrug it off, go home and put them back on the car. A couple days later one is low, and won't hold air. Back to the shop, reseat the egde, took extra care to get a clean seal. Still wont hold air. Back to the shop. Finally, "Found the leak, the wheel has an internal crack forming."

Ok. Maybe thats why PO had tubes in all 4?... but the other 3 seem to be holding fine...

Any tips on fixing the wheel up to hold air? Tried some epoxy over the visible crack, but that didn't seem to help. So we are thinking, back to running a tube just in this one wheel (its a front). Car isn't really driven enough or long distance that this should be an issue. The issue, 'normal' automotive tubes don't seem to have the valve 'clocked' right. It doesn't reach the stem hole in the wheel. Obviously whatever tubes were in prior fit well enough. But it was so long we don't know what they were, the shop has tossed the old tubes by now.

So i have really 2 questions.

1) Does any one know what type/make/model tube would have been used on a Halibrand that would fit i guess the "non-typical" valve location. And a source to get another one.

or

2) Any tip or advice on how to seal the porous internal face of the wheel to make it reasonably airtight? Is it even possible? I keep reading murmurs of various "epoxies" or "enamel" tricks on old hot rod forums, but no specifics, and I can't find any indication on what or how exactly to approach that.

My mechanic who I trust reasonably well, has exhausted his own knowledge on the matter, and has apparently called every wheel shop in town, receiving the same answer from each. "Magnesium? We're not touching them."

Have any of your encountered/successfully dealt with this issue? I'm happy for any advice.