Hi, a couple of weeks ago I had problems with my 90's diesel freezing. After a bit of searching I came across "stanadyne performance formula" diesel additive which is supposed to help prevent diesel gelling and waxing.
I bought a 235 ml bottle to try, which treats 120 litres. It can be bought online at www.dieselpartsdirect.co.uk, although I managed to get mine at my local LR agents. It is a lot cheaper on the net.
Hope this maybe some use. Regards, rocky