Maybe take a piece of safety wire and make a small loop (so you don't poke at the vacuum pump check valve). See if you can fish something out that way.
Pulling the front cover is easy enough. But, if you do, be sure to get a rebuild kit. It is easy enough to do. Especially if you are going to pull the front cover off. If you are pulling the cover, rebuilding the pump (minus the bearing) only adds about 10 minutes to pull the piston and install new o-rings and check valves.
This thread made me a little paranoid because I drive the car so much. I actually pulled my main vacuum line this morning, checked it for leaks (again) and inspected the check valve on top of the pump (again). It is all still in there... Whew...
