You say your problem is with the cable operation, but it is possible to buy a flush valve where the operating mechanism is directly on top of the valve and alines with the hole in the top of the cistern, you will have to remove your cistern to install it and the twin buttons are fitted through the cistern lid and operate directly on the flush valve. You need to check your cistern before buying a new valve but if the button is directly over the flush valve you should be alright. Make sure whatever one you buy can be serviced in situ as you know, the rubber seals can start letting by esp if your in a hard water area.
BTW Ive not had any problems with the Torbeck type fill valves Ive fitted, however if you have low water pressure then a ball valve fills faster.
Steve.