Did the OK button on your original RM-F01 remote stop working? Mine did. Started working intermittently, then conked out altogether. I was loathe to buy a new remote, so decided it was worth a shot taking the old remote apart.
Friends, after removing the batteries I used a sharp knife to carefully prise apart the two halves of the remote along the seam down one side. This is the only way to do it, there are no screws. You will damage the plastic a little in doing this. Like mine, you may break off a couple of the plastic tabs. However, in doing this I successfully took it apart. Happily the little springs in the battery compartment slide out by themselves so the two halves of the remote aren't connected. Once the back of the remote is off you will see the brown circuit board. Carefully free this from the clips on the front of the remote. I can testify that it bends sufficiently without breaking. The circuit board will come free. The button membrane may come free too - not a problem, it's all in one piece and you can easily refit the buttons through their holes later.
Now locate the circuit board location where the OK button makes contact - on mine it was marked with the number 42. Now here's the crazy bit. You need to clean that location on the circuit board. Use a little isopropyl alcohol on a cloth if you have it. I had run out so I just used vodka. I know, it's not the right stuff, it'll leave a residue etc. I don't care, I'm just trying to save 20 quid here. Afterwards I used a clean cloth and cleaned and dried the hell out of the circuit board. Then I just reassembled it all and snapped the remote back together. It clipped back together fine. Then I drank the rest of the vodka.
And now my OK button is fully functional again! I think this approach is worth a shot if you don't want to give Humax any more money for their stupid remote.