The relevant Lycoming Mandatory Service Bulletin is 518D and relates to a possibly faulty Thermostatic Oil Cooler Bypass Valve.
The problem is that a crimp nut on the end of the valve that is located inside the engine can come loose and drop into the engine accessory case causing engine damage. Oh ooh.
The Mandatory Bulletin outlines a procedure for removing the valve and checking the crimp nut. If the valve nut fails the check the Bulletin calls for it to be replaced with a current model of approved valve as stipulated in Lycoming Service Instruction # 1565.
Service Instruction #1565 calls for the approved valve replacement to be a part no. 53E22144. In other words if you have a valve with part no. 53E22144 in your engine then you have no problem and the Mandatory Bulletin is not applicable.
To determine the part no of your valve you should look in the Engine Log that came with your engine. It should contain a list of all components and the relevant part numbers (including the valve). Failing that you will need to examine the valve in your engine to determine its part no.
However, as a rough guideline, my AeroSport IO360 was purchased new in February 2008 and came with the current (approved) valve part no 53E22144 so I am assuming that any new engine purchased after that date will likely also have the approved valve....unless of course the "manufacturer" used very old valve stock.