Your pain sounds almost as different from my pain as can be, but I get a lot of spasms too. I've tried every muscle relaxant on the American market, as well as all the benzos. I don't have any neuropathic pain but drs in the US were determined to diagnose me with it so they wouldn't have to face the fact that my pain is entirely muscoskeletal in origin, and thus my medication options are much more limited. So I've tried gabapentin, baclofen, and a bunch of other neuropathic pain meds, none of which helped alas.
The only non-benzo muscle relaxants that help me at all are Soma and Flexeril (tizanidine), with the former being much more useful. But neither helps as much as diazepam. Other benzos don't help at all, though I haven't tried temazepam as it's not used in the US. Thus why I call diaz my wonder drug. I've been taking it pretty much daily for 5 years and I've been able to keep my tolerance down so that I'm taking the same amount I did 5 years ago, and it continues to be effective.
There is significant literature that shows that diazepam has strong muscle relaxant properties, perhaps even the strongest out of all drugs across all classes. Its longevity and minimal side effects make it a good option for constant/chronic muscle tension and spasticity. I've never suffered WD symptoms either; it's a lot safer than other benzos in that regard.
I've found if you tell a Dr you've had it prescribed before & found it very helpful, generally getting a script isn't difficult.
This new drug I'm on, flurpirtine, is really great so far, and apparently it's good for neuropathic pain as well as muscoskeletal. It's not abuseable so you shouldn't have a problem getting it. When I'm fully off the diazepam & have been on the flurpirtine longer I'll report back.