I have experienced this before on a car with Auto transmission that has been stored for many years. You want to drop the pan and remove the filter and the small filter gasket. Since you live in the United Kingdom find a Renault parts distributor and ask for a Renault 30 TX/Ts filter and gasket kit. The American DeLorean parts and service center has them as well. Once you have the pan removed, 1) Clean up the old fluid. 2) Spray some "Liquid Wrench on the INSIDE pan threads of the plug, as well as around the outside diameter. 3) Let "Liquid Wrench" work itself into the threads and SLOWLY use the 3/8 drive to remove the plug...make sure that the "Liquid Wrench" is liberally applied to the threads...you do not want to strip the pan & plug. Best Wishes, Michael R. Pack