What oil did you use Lucas. Did you pre-sand or use Netrol and jet wash prior to your oil being applied.
It may certainly be the salts in the water that has reacted with the oil. It would be wise to strip this back – try a test area with Netrol but I feel you may need Aquanett or Dilunett to strip back first (Then essential to neutralise with NetTrol). This would actually benefit if this hasn’t already been done.
Best of Luck
Karl