Try this:
http://www.modelsport.co.uk/hpi-sb-5...roducts/363465
I was given one of these under warranty when the original SF-50 servo (a re-badged Hitec HS645MG) in my HPI Vorza stripped its gears.
The SB-5 is half the price, has the same torque but twice the speed!!
I can't comment on long-term reliability because I haven't had it very long but it feels solid.