On our last trip I had to urgently put 1 litre of Castrol GTX diesel 15W 40 into my td42 which already had Penrite HPR diesel 20W 60.

I'm more then happy to dump the lot and start again but should I?

The Penrite was only put in 500km ago with new filters so should I just leave it or just keep the oil filters on and just dump it and start again?