Two types of oil sump were fitted to TR250, 5 and 6. Part number 307834 and 307836 the difference being the position of the drain plug which was initially at the centre of the front face and later moved to the rear of the left hand side.
The 2.5 litre sump differs from the 2.0 litre sump in that whereas the 2.0 litre sump is flat in the shallow portion, the 2.5 litre part slopes slightly to make way for the extra throw of the crankshaft. This taper has the added advantage of promoting oil flow back to the main sump.

New steel sumps are not available so the alternatives are a second hand original part, an aluminium or a magnesium replacement.