1,3,4,2.

[Ivangardiner]

Maybe the replacement distributor has a cracked cap.  Also, my Bedford camper had an enforced 3 months parked outside, and the contacts inside the cap got quite corroded.  My theory is that, with the one contact which was corroded worse than all the others the spark would say "too hard to get across there, I'll go to the next nearest one instead".  Fitted a new cap and no more problems.  Still only a theory of course...