This could apply to any remote that used the plastic tactile blister layer with carbon pads, not just Roku.
In my case the most often "OK" button on my old remote required increasing force to work. The problem is that over time the printed carbon on the clear plastic part has worn away and is not conductive.
First I disassembled the remote. There are many guides on how to disassemble the remotes, so I will not cover that here.
Using scissors I cut out one of the blisters from the bottom piece. Square, about the width of the distance between two buttons. These are for the 4 for instant access to Netflix, Hulu, and such that I never use so no loss of functionality for me. I simply dabbed a small amount of superglue on each corner and overlaid it on the circuit board side of the OK button. The domes nest together for perfect alignment. Reassemble. The button works effortlessly now. Saved me $20 though it did take about 15 minutes.