All four doors on my 260E make a creaking sound when opened and closed. I sprayed WD40 into the hinges and door stop and the sound just changed into a loud groan. How should the doors be lubricated and what should I use? The doors stops seem to be making the noise and they are not easily accessed.

The doors hinges have grease fittings but take a special type of needle type injector for the grease.

The door check was redesigned just before your car was made and the new design is about impossible to lube from the outside. It uses two balls that retract back into the same tube which is verticle and inside the check itself. We use a product made by Wurth called HHS. It is originally about the consistancy of WD40 which can creap into and up through surface tension. After about a minute it thickens to a coating almost as thick as wheel bearing grease.

The problem is hopefully in the door check as an abused hinge is hard to repair.

The door check mechanism is what is causing your noise unfortunatley the two ball bearings corroade and may even have flat spots, no amount of grease will cure this fault.
The unit is easily removed once the doortrim is removed the balls could be replaced with new ones from a bearing supplier but it is probably easier to just fit new units they are not very expensive, just make sure you pack them with heavy grease before fitting.
Cheers Linds Cornwall UK