issue with ARB rear air-locker

Hi, back in May this year I had a LOT of work done on my Toyota Hilux 1998 dual cab LN167 which included the fitment of a rear air-locker, at an ARB store.
.
Since the fitment of the rear locker, it sometimes does not engage, I.E when you activate the compressor and the locker, the compressed air instead of locking the rear diff it blows the compressed air out through the diff breather.
.
I've now had it back to the ARB store three times in the last three weeks. They removed the diff each time and replaced the seals in the locker.
.
When I took it back again today, I was told that sometimes the locking ring that slides over the spider gears, does not 'line-up" and this can cause the unit not to seal completely.
.
I was told to correct this problem that I should drive a short distance forward so the locking ring can 'line-up" with the spider gears. Once it has "lined-up" the locking ring will engage and complete the seal.
.
Has anyone else had a problem like this with their air-locker.
.
Thanks
Dave