if the product came with a claim of a 5 year warranty, then i would think you are fairly solid ground; they have specifically guaranteed a lifetime that you are within, so your claim will just have to show that any wear and tear is reasonable and that the product was not fit for purpose. The multiple repairs in that time frame is suggestive of a reoccurant problem.
Just make sure you have all the paperwork from all the previous repairs. The tribunal process is fairly straight forward.