Mercedes has revealed that the hydraulic leak on Lewis Hamilton's car that forced the team into a frantic repair job before the Canadian Grand Prix was linked to a throttle actuator.
While the leak was discovered after Saturday's qualifying session, F1's parc fermé rules prevented Mercedes from identifying the source of the issue, or its severity, until Sunday morning.
Needless to say, the Silver Arrows team's crews, and Hamilton, left the track on Saturday in a worried state.
"We had some issues with Lewis's car before the race and this actually became apparent after qualifying," said trackside engineering director Andrew Shovlin in Mercedes post-race Pure Pitwall debrief.
"We dropped the floor, we noticed there was some oil on the floor, so somewhere there was a leak. We could also see on the data we were losing some hydraulic pressure.
"The issue is that the cars are then in parc fermé overnight, we are not allowed to touch them or to investigate it further.
"So, that investigation moved to Sunday morning, when we are allowed to access the cars again, the mechanics can work on them."
A proper diagnosis led to the massive task of removing the W10's power unit and replacing several parts of the hydraulic system, with only hours to spare.
"We had to take the power unit out. We traced the leak to the throttle actuator, and then we made a request to the FIA to change the throttle actuator and some of the associated hydraulics," added Shovlin.
"So, that work was quite a big job though, there's a lot to do within that. And it was pretty tight to get Lewis's car back together for the start of the race.
"Now, we are fairly happy we can do the work in that time. The issue when you have an unknown fault or a leak is you don't know how long it is going to take you to find it, to identify it. We were able to get the car back together.
"Where we were at risk was if we then fired up and we found another problem, if the engine had to come out again, that's when we would've got short on time and perhaps not even been able to start the race.
"But, it was a great job by all the mechanics involved and quite happily the car was back together in time and finished the race successfully."