MOT Failure Handbrake

 Hi All
 My 1998 mk1 1.8i has just failed the MOT on poor handbrake on the offside. When I purchased the car the handbrake on the nearside wasn’t connected and was only connected on the offside.
I have replaced both the rear discs and pads and reconnected the cable to the nearside
All other brake tests were passed fine therefore is it possible that the cable on the offside could have stretched and this is what is giving the poor result on that side. The garage are talking about a new cailper for the offside but if the cailper was knackered wouldn’t the car also fail on footbrake ?
Any advice greatly received 

 There’s a good write upon rear brakes here 

Thanks for the response.

I’ll have a read [;)]