nice puddle of oil under the van in the car park.

closer inspection reveals a steady drip from the base of the oil filler tube...and rather alot of crud around it.
Have bought oil to top up and get home. Saturday's plans may have changed

so....a good clean up and see what's what I guess.
If it is that, is tightening likely to work, or is some sort of gasket required?
as always, any help appreciated!
Em
xxx