A hotter plug might work for now. There are several reasons why a plug oils, and once oiled, they seldom clear themselves.
Try a compression test - if that's OK it might be a valve stem oil seal.
The BL A Series engine was prone to oiling number 3 cylinder. I once had a valve fail and the plug oiled immediately. Despite several attempts at cleaning of course, it had no effect. Sometimes if the plug wets on a cold start it won't self clear, and will appear to be oiled. If you suspect that, then try warming the plug on the gas ring before starting. That problem may be the choke, but could also be a compression problem.
It's a case of trying one thing at a time.
According to the NGK website - Morgan 4/4 1985 is BCP6E, Escort 1600 1985 is BCPR6E, or Iridium plugs for both - (Expensive) is BCPR6EIX
