Tok a bit of tracking down, but I did find there had been a firmware upgrade for the audio chip. It may have been due to support for very old audio systems getting dropped from Linux kernel or from sdl, in ant case there was an updated firmware in AUR which solved the problem of intermittent crashes after 5 hours, so urw is now playable.
There is still a small problem, when exiting urw there is an audio buffer underrun every time, but this does not seem to affect anything though it does seem to be a urw problem. I also have a different audio problem with widelands not exiting cleanly, it does not report the buffer underrun but does kill the unresponsive audio after 5 seconds, again it does not affect playing and currently there is a sdl audio code review occuring in widelands which may solve the solution.