Hi Allan.  We have not been so lucky.  Off the top of my head, we lost most of the XMT 300s in our former 8 pack due to weld output that would drop off during welding.  If I recall at least one had capacitor problems.  We have 1 or 2 that are still functional.  Digital meters failed in most of our Dimension 652s at the 3-4 year mark.  A brand new Dimension 652 we bought w/ low OCV feature would, at random times during starts, go to full output and basically explode the end of the contact tip off with a loud POW!!! ... scared the crap out me.  Several brand new Iron Guns had their triggers go non-op within minutes or hours of going into service when the wires inside the gun handles broke in half.  A Millermatic had a catastrophic internal short because fasteners on the large capacitors inside were loose - total loss.  A second one had a capacitor failure for no apparent reason.  A XMT 456 recently suffered a small internal explosion and several minutes of smoke - total loss.  A digital display Sync 250 lost its lift arc and later its high freq starting capability.  Our older Sync 250 suffered a meltdown - total loss.  A Dynasty 300 had an internal meltdown for unknown reasons - total loss.  A second Dynasty 300 has an intermittent gas shielding issue, assume the solenoid is TU.  A XMT 350 Mpa lost a board.  A second XMT 350 Mpa lost its pulse capability for GMAW.  A 350P intermittently goes into “tip save” mode while trying to weld.

Our CST 250s have seen loads of use and have been bullet proof, and so has our Dynasty 700 (thank goodness!), though the 700 isn't used too hard too often.  We also have an older Sync 350 that has been plugging along for a couple decades or so.

Not sure why some machines have been problematic.  The problems span over use in two different shops.  The machines have always been blown out regularly.

I have been switching over to Lincoln Flex Tec 450s for multi-process power sources.  Started several years ago.  So far pretty good.  We now have 3 4-packs and one loose machine.  One 4-pack came in with set screws in the primary power junction box that weren't tightened at the factory.  This lead to a popped fuse.  But we fixed that easily and no damage was done.  One power source had the digital display incorrectly installed so it was very crooked - that required opening up the machine, unplugging the display, and plugging it back in to the panel face with the proper orientation.  12 of the 13 are in use outside (covered).  They have all operated flawlessly.  Great lift arc start on TIG, and the best (shortest and softest) arc breaking when snapping out that I can recall on any power source.  CV gasless setting is great with T-8 wires.  Excellent arc for pipe with both 6010 and all diameters of 7018.  I would like to get a couple more 4-packs. 

Time will tell if the Flex Tecs hold up, but so far we only have had 2 Lincoln failures at our facility in the 14 years I have been here. One has been with an Invertec 350 w pulse programming - it lost a board.  The other was with a newer Precision TIG 375 - it had a bad main power switch that flopped down on its own, it was replaced under warranty.  We retired 3 or 4 DC600s from our covered outside weld area that still worked perfectly when we sold them.  Great machines for structural, but horrible for pipe as they had no Dig / Arc control for use with stick and scratch TIG.  We are still using the same LN25s I bought 10 - 14 years ago, never a problem.

Not too impressed with Lincoln's Power Mig 255 XTs though.  The arc quality doesn't match the typical Millermatic, not even the little stepped 210, with .030" steel wire.  Also, the poor discrimination of the spot timer adjustment knob is irritating. 

Anyhow I am leaning towards the Pipe Works only because they seem to be the pick of the pipe shops for which we are training for employment.