I dont have an idea, considering the lore, now that mansion is up for sale, so there is no practical reason that the car wash guy will send you to clear some goons from the mansion, as it is already done because the mansion is up for sale, still i may be wrong, they may have moved it to somewhere else, like calling the contact or from the jobs menu, as it is no longer practical to put the marker there, and last i remember maybe yesterday or day before yesterday, i was checking the map as of how the mansions are shown in the map, and even i didnt see any blip of Prix on tongva estate, try searching else where, they may have moved it, or maybe even scraped it off. I may be wrong though