M/As can be a huge cash cow for the maintainer. The trick is getting enough business to support your staff, parts etc and then being sure you are priced right. IBM used to be a "lease only" business, then the government made them sell their equipment in the 70s. It turned out they were making a lot more money in the M/A business than they did with the leases and they were not carrying all that rapidly depreciating inventory.
The business went away when things lasted longer without a call than their useful life. We installed a water cooled 3090 (old time mainframe) in Ft Myers that ran for 5 years and never had a call. That M/A was pure gravy.
