My ZT was an SMG car. The one previous owner said he bought it to replace a Stag that rusted away. The ZT didn't do it for him (not really the same type of car), so he sold it. When he bought it from SMG, delivery mileage, it had all the tyres, belts, filters and fluids renewed. The only real age related deterioration I found on it was the Shannon tube had rotted. Also the windscreen cracked within weeks of getting it, I'm not sure why. I'll keep my fingers crossed that the other seals keep going, but I was well pleased to get a vgc low mileage ZT at a good price.
I've browsed around SMG when picking up OEM parts and agree their cars are well above the market rate. However it seems some people are prepared to pay their rates for our favorite brand and SMG do seem to do a thorough delivery service.