The proper lube will take care of the problem but the trick to have it go away for ever is to adjust the strikers perfect if not you will be using lube every so often and put it on your clothes some day when you will touch there with out intending too.
I have the same model and year and this problem drove me nuts the first few months and I off road a lot which makes the dust stick to the lube no matter what you use.
Spare is no issue make sure is tight.
When you are adjusting the strikers make the adjustments on the part that is on the truck not the door slightly tight but not tight enough where it can move when the other comes into contact with it when you close the door.
Be inside the truck when the door gets closed and you can see and assist that it does not move when you open the door again in order to get it tight.
Have the person that opens the door to exert a little force upwards on the handle as he or she is opening the door.
After all tight go on a drive and test on corners with bumps if it still there...I forget which way but one side left or right would do the most sqeeking.
After you get it where it sqeeks very little rarely or almost none just a very small amount of vlads lube will be ok to keep it totally quiet and with time and another 20k miles it will go away for ever even if you do not keep on lubing it
Your door latches will do that also sometimes and they will be fine with a very small amount of lube.
Mercedes bearing grease is awesome and your hood will need it some day also.
Got 40k on mine with tons of off road and I have zero squeaks and rattles anywhere
Best of luck
Mario
