Just resurrecting this topic, as it obviously is an issue on all Omegas (and other modern vehicles for that matter), and any second hand switch / button assemblies are likely to have gone the same way.
I have just put one of my Omegas back on the road after a long period of being laid up. The driver and passenger window switches, plus the boot release button had gone extremely sticky - almost gooey in fact. They weren't like that prior to the car being laid up, and as it wasn't being used, it obviously wasn't sticky fingers that had caused it - it was most likely a combination of of sunlight and general degrading of the 'soft touch' coating.
I tried Ambersill Tar Spot remover followed by Ambersill Foaming Upholstery cleaner, as recommended, which had no effect on the sticky surface whatsoever. The problem is that harsh cleaners can remove the white symbol on the surface if not extremely careful. On the boot button the symbol can easily be damaged, so I decided to use a product called 'Non Sticky Sticky Stuff Remover', which is primarily intended for label residue etc, and although it took a lot of rubbing and a lot of patience, the boot switch has now come up a treat, and the symbol is undamaged.
On the window switch, I tried all sorts - the above Non Sticky Stuff remover, White Spirit, Electrical Switch cleaner, Solvent cleaner, Ambersill upholstery cleaner, WD40, even brake cleaner, but none of the above worked or even sniffed at the residue.
In the end, similarly to Nail Varnish remover that has been suggested previously, I used General Purpose thinners, which removed the sticky soft touch coating with some careful but vigorous rubbing, leaving the hard plastic finish underneath. It is a satin finish, but almost smooth, but looks excellent. I must stress that you have to be very very careful with the areas between the individual switches, and the L/R mirror control button, or the thinners / Nail Varnish remover will take the black colour off the edges, and the symbol will be lost if the thinners comes into contact with it. I used a cotton bud for the difficult to reach areas, and the cloth wrapped round a thin screwdriver to apply the required effort to remove the coating.
I did actually loose a little bit of the edge of the circular mirror control button, but some matt black blackboard paint with a fine brush on the affected area and it is now hardly noticeable.
Hope that helps anyone with sticky switches!