I just checked Munich's official homepage, and in an article about lockers they say that in Munich's Main Station and East Station there are short-time and long-time lockers available, short time meaning max. 3 days and long-time min. a month. They come in three sizes, small, medium and jumbo. The small one (short-time) costs 1 Euro for 24 hours, the medium one 1.50 Euro and the large one 2 Euros for 24 hrs.
If you don't want to use lockers for some reason, apparently there's a service where they will take and guard your stuff for you, but it costs 2.05 Euro per piece of luggage and per day.
I might be able to get a map of the station - if you want it, let me know.
