From my experiences with the Boss sewing machines I´d advice you to find an old model, cast iron Boss. I have had two aluminium frame machines , the first one sounded like it was filled with gravel right out of the box, and it didn´t work. After some problems I got a new one and it functioned a couple of weeks, then the jump foot mechanism broke, which caused the needle foot to break. I ordered new parts, put it together and sold it. Then I managed to find a used cast iron Boss ( it was not used, as the owner had no idea on adjusting tensions!) and it is like a Swiss watch, no malfunctions, it sews without problems year after year . The only thing I´ve done to it is installing a take up lever spring, to keep tension of the top thread during the whole sewing cycle. (part # AR-49)
The difference between the old Boss and the "upgraded" version: Old Boss has a cast iron frame and the inner parts are made of machined steel . The new model has a aluminium frame and the inner parts are made of zink castings, a difference like day and night!
(Also found out that Tippmanns customer service ends at the US border, sad but true!)
/ Knut