A 2007 Probably has a EPDM (rubber) roof membrane. Later models changed to TPO (plastic) roof membrane around the 2010-2013 years.
You can verify the type of roof membrane on your Sprinter by removing the inside vent fascia from one of the roof vents. There are 4 screws holding it in place. You'll also need to remove the vent handle by removing the center screw. With the fascia removed, you can see the edge of the roof membrane where it was cut, pulled inside and stapled to the wood structure. Look at the underside of that membrane. If the top is white and the bottom is black, it's EPDM. TPO membrane is typically the same color on both sides and some has a "fiber backing" on the underside.
If your roof is EPDM, then get DICOR self leveling sealant at any RV store. DO NOT USE SILICONE or any product with silicone in it !!!!! Clean the roof thoroughly, remove any loose or damaged sealant and apply a new coat over the old, overlapping the edges so the new sealant covers any area where you removed sealant and covers all the "old edges". Allow the sealant to dry, it will take 3 or 4 days to lose the tacky feeling.
You can download the DICOR roof care handbook here: https://dicorproducts.com/rudys-down...care-handbook/