hi buddy i ran my 95 tdi on good quality mineral based oil 10w40 grade i would keep away from semi or full synthetic if it has not had this oil type from new as you can end up with some nasty oil leaks from some engine seals when the disco has had synthetic after mineral as the synthetic has far better cleaning properties than mineral oils and can wash seals to clean where varnish and other crud has built up and helps keep a good seal if you can get it morris pil is very good,cheers phil