Honestly that gun is the epitome of simplicity. You could learn the intricacy of that firearm by doing it yourself. There isn't much for moving parts and very few rubber/o-ring type parts (one small o-ring on the bolt if memory serves me correct). You'd spend a fraction of the cost doing it yourself. With the original SBE/M1's the most complex part of the process is disassembling the recoil spring tube becasue the nut that holds the spring inside and the stock on is loctite'd on..... sometimes with red, sometimes with blue but if it's red a quick minute and a half heating gently with a blowtorch will free it up. then it's just the spring inside that might need replacing (<$15 wolff spring) and if salt was really hard on it the tube itself can be replaced. The bolt comes apart very easily and all parts are usually readily avail at midway. The magazine is a spring and stopper...... literally thats it.
I know that's not what you asked, and that still won't help you with getting it dipped but working on these guns specifically is very easy. Things like balancing a checkbook or changing oil on your truck are more difficult than working on a benelli. Sorry for the rant but unbeknowst to me I just had a buddy take his original sbe into a smith for what he called a "tune up". The guy charged him $175 to clean literally the most simple autoloader ever......