Abstract: An internet search on the use of Blu-Tack®, a flexible tacky polymer, as a possible transmission oil stop leak for defective or old gearboxes, showed that there was no evidence to support this hypothesis. Ten preliminary tests involved heating a piece of Blu-Tack attached to a stainless steel kettle for not less than 30 minutes at around 100°C each time. As the Blu-Tack retained the same rubbery and sticky properties it was then decided to investigate whether it can stop gearbox oil leaks on two cars: a relatively new car and an old one. A reasonable piece of Blu-Tack was worked into a long cylindrical strip and pressed firmly using the fingers onto the trouble area so as to form a flat strip approximately 1 cm wide thus covering completely the defective rubber seal or gasket. After ten months and more than 3,000 km of road testing, the putty remained intact and no oil smears were detected. On the much older car with cardboard gaskets, the same procedure was applied and Blu-Tack was again an effective, exterior stop leak. This study provides a platform for further scientific experiments on the use of Blu-Tack for stopping transmission fluid leaks. It is also recommended to investigation whether Blu-Tack can stop engine oil leaks.