Q: Are these oil leak problems related?

If the oil filter housing is integral to the oil cooler, or the housing had to be removed to service the cooler, a professional mechanic with knowledge of the limited service life of rubber seals would have absolutely (guaranteed) replaced the filter housing gasket that you are now belatedly finding leaks. However, if the leaking gasket is in an assembly that was not touched, or is not part of the cooler, they might be on reasonable grounds to have not fooled with it. These cooler configurations vary (from Mercedes Benz model to model) so, having the advice I just gave, you can just simply ask them what configuration you have and go from there. The bottom line is, if indeed, the gasket that is presently leaking was "right in front of them" while they did the warranty work, it should have been replaced simply as a matter of course. Indeed, the weak link on modern engines has become gaskets and seals. The engine will mechanically far outlast the gasket and seals but the problem is to replace all of them (once they all leak) you have to literally take the engine out of the car and take it apart just to put all new seals in. Please let us know how we can help further on this issue.