Hello. I recently performed the 3,000 mile oil and oil filter change on my F70 1990 Non-Turbo 'trak. Since then the oil pressure warning lamp stays on for about 10-15 seconds when I start up after sitting for a day+. Whereas before it went off in under 5 seconds. I used the same filter and mineral oil as previous oil changes. After I refilled the engine with oil I checked under the truck and discovered the bung was leaking, so I had to drain the new oil out and fix the bung. I didn't have a clean container to put this in so I used another 5 litres of brand new oil. As a result the oil in the engine is still clear and clean after about 200 miles. I wonder if this "flushing out" with new oil has cause the low pressure at start up due to clearing worn clearances previously blocked by sludge ect.