Dell 3010cn - missing line of print down the right had side 1cm in

After replacing a new set of toners in my old 3010cn it messed up bluring and missing a line down the right hand side about 1 cm in form the edge. Next the fuser units would not work and said it needed replacing. So....

Rather than wasting the money I spend on the new set of toners I purchased the same unit again.

On the first set of prints the line was still there in the same place !!!! I contacted the provider who had not heard of this issue and then sent me a new drum then a new fuser unit. Still a missing line.

They have now sent me a new unit, which afer the first 2 pages printed fine, I thought great all good now and set to print 20 pages of the same, only for the first 5 to be ok then - yep the missing line which then got bigger to miss the whole of the 0.5cm from the right had side.

This is printing on A4 with the setting on A4.

Can anyone shead any light on this error and know how to fix it??

Please help.