You have to be careful which exact panel you have, R8/Plus or Excel is not compatible with the standard LCD Premier keypad.
A 412/418 I believe should be compatible, but they are not a common panel in the UK.
The plastic casing is actually over the top of the silicone buttons on your new keypad, must be a pretty old keypad if it is silicone buttons only.
Keypads have a data connection they do not store data, LCD, LCDL LCDP LCDLP are interchangeable but have different features, prox, large screen, both etc.