I think the 740 is all metal under the base, the only gear I have seen cracked is these models is the white plastic gear turning the cam stack. They often last 40 years before there's anything wrong with them, and are well worth the time and effort it takes to replace them. I have a 730 which generally is the same machine above the base. The bobbin case, race, hook and turning parts under the base are much more solid on a 740 and different. It is a rotary hook design.
The 730 has one or two plastic gears in the freearm, but it doesn't apply to the 740. Even these tend to last a long time, but like any other part they can get damaged. I have seen quite a few old Berninas the last years and they are mostly runnig fine, even the ones with very worn finish. My 730 is my most trouble free and well behaved zigzagger. The motor on the 740 has at least double the specs than the freearm versions.
Another thing I have noticed with the 740 is it's often greased way too much. I don't think Bernina recommended anything but oil on any of the gears and turning parts on it.
Last edited by Mickey2; 11-29-2017 at 03:55 PM.