There is also the UKC8764 dust cap which is basically the same as the UKC3159 but the UKC8764 needs some slots cut in it to match those in the UKC3159. I think the UKC8764 was used on the LT77 remote. I used one on my R380 box last year. It is listed by
http://mgrovergenuine.co.uk/ but currently out of stock, may be worth asking them if they will get stock.