Most common problems were power supplies and perpieral related. Serial lines drivers and recievers were common failures as well but in the mill we usualy had long lines and occasional ground faults to deal with. If the machine is kept reasonably cool it's a rock. Within DEC 750s were very common and after they were less in vogue for actual use they serves lat, mop and routing service as they required near zero attention if any at all. I have a bigger sample size to look at from being inside DEC. the gate arrays are as relaible or more so than any other chip and the likelyhood of failure is highest for chips that talk off the board this being due to electrical stress (drivers) and ESD from handling the board. Theother group of possible failures is in ram arrays as there are so many it's statisiclly possible to see a part fail. Allison