Poorly built box in my opinion.
I had my RST box go so I got a rebuild and it did this straight away, took it back and they replaced the selector and 5th gear and it lasted 200 miles.
Just got myself a 2nd hand box that hadn't been touched.
I must have expected too much for my 150 quid.
If I ever have another RST I will without hesitation have one of CTS (Bernie/Gearboxmans) Stg 1 boxes at the very least.
Jake