I have had an hl-1, and hl-2 (sl-20) since 1998 and Until a year ago I did only 316L stainless some inconel, and very little hastaloy. I have yet to "wear out " my machine. the hl-2 has even been thru some crashes but still runs like a champ. I use a 1.875" ceramet coolant fed drill on at least 1/2 of the jobs. so it can push it.. I also did ALOT of stainless hex (and if this isn't hell on a machine I don't know what is) Oh and I have an sl30 Its .... better!
I do primarily aluminum now and personaly I think do to the " chip float" factor aluminum maybe harder on a machine than any other material. Man that stuff gets everywhere, it even seams to wind up in sealed containers. when I ran stainless the shop was very clean and not many chips anywhere. Now with alum. we are in the crunchy bug like snow shop.
but seriously. the machines can handle it fine.
I bought one of my machines from a guy that couldn't get it to "hold tolerance" I haven't had any problems but then again I know what I am doing (still learning though). Got a REALY GOOD price on it though! hehehh I love the guys that always think cheap is junk.
ps: He bought a yasada so I sure he is happy with his new machine, because he bought one of the best. But I bet his pocketbook is realy hating it!
If you stalled the machines maybe your just pushing it too hard but without specifics no one can give you an accurate reply.
Feed, speed, cooant, material, depth of cut that kind thing