I think you are stuck with buying a Mulfab one Niall. Wasn't aware that MMC sold aluminium ones. If that's the case though likely they are made by Mulfab which is the usual after market choice now. Suggest you get price of each first though, but probably better to buy direct from manufacturer.
Regarding longevity remember you have an eight year old car now with the low mileage having less of a bearing.
IIRC Simon made Aluminium Rads for the factory, so wouldn't be surprised if they went to Mulfab in his absence.
