Apollo 12 landed right next to the Surveyor 3 lander, and the astronauts removed a few pieces from it and returned with them. When NASA disassembled the video camera later they found microorganisms still alive on the device.
This is not as exciting as the notion that some bacteria might have survived for years inside the lander on the Lunar surface, but it still illustrates the risks of failing to maintain a proper clean room environment.
This article asserts that this was the result of a clean room failure after the parts were returned to Earth: https://www.space.com/11536-moon-microbe-mystery-solved-apol....
This is not as exciting as the notion that some bacteria might have survived for years inside the lander on the Lunar surface, but it still illustrates the risks of failing to maintain a proper clean room environment.