at the moment, i dont like to buy another guruplug with the same failor, in addition i don't know if i shoud buy a guruplug again.
But i will try to replace the GL850 when my delivery from China will arrive. I found a supplier at aliexpress that delivers 5 pices for 8$ inc. shipping to germany. If you like i could send you one of it by mail (the non-e one ;-)?
What's the failure of your guruplug?. Is not seeing anything connected to the usbs?. Have you checked that the u4 (GL850) does not shows the V33?. If so, if you fix the problem by changing the chip, I will be very happy to get one!
Hope you have luck!. Keep in touch,