I'll Fix It - S4-E2
Continuity mistake: While Roy and Johnny are under the house with the oil eruption trying to free the trapped man, they get covered in black oil and mud even though they're wearing turnout coats. It drips down their necks and their pants are soaked with it. When they get to Rampart with the victim, Roy says that he and John should get washed up, but when they talk to Dixie they haven't just washed up, their clothes are now impossibly spotless.