Well yes, it could be a vacuum leak. One should always look for obvious ones. The minute a mechanic tries to sell you new manifold gaskets though (a reasonably big job), tell them to jump in the lake until you've exhausted every other possible answer.

On your care there are several items that affect this. Also note that the idle surging and the startup issue may be two different issues.

1) Cold Start Valve. This is a ~$100 part that is easy to change.

2) idle control valve may be dirty or faulty. Bought aftermarket (VDO), I don't remember if FastLane here has it but it should be your first shot if replacing it, or autopartsauthority.com for $240. Easier to change than oil. Cost $750 from MB though so must be bought aftermarket. It is cleaned-out with carborator cleaner, search on the forum here for any tips on that.

3) Yes indeed look for all oil leaks

4) The fuel filter may indeed be dirty and require replacement but I doubt that all of these problems are caused by the filter. The oscillating idle is probably not caused by fuel delivery from the pump/filter but instead is related to control of the fuel injection system. I assume performance is good anyway?

5) So you should look for vacuum leaks in all places, including around the fuel injectors. I have some past posts on that (click on my ID) and also search for vacuum leaks, finding, etc. Be very careful if you use anything combustible. Never ever spray anything on the manifold you could burn-up the car. At the same time, using this method I found a large vacuum leak left by an inept mechanic after work done to solve some other issue.