Deliverance
Bloodhound Mk 2 (all the stuff I worked on came out of Ferranti at Wythenshawe), though most of the radar stuff was done at Edinburgh.
The US system was part of that piece of junk better known as Radar Type 93.
Leon and Courtney have hit the nail on the head, Quality and Experience of technical staff plays wonders or disaster on the serviceability of radar equipment, be it on the line, in the 2nd line workshop or at a deeper level. Have one or two wizz kids of JNCO's or OR's and a good Trade Manager on your repair organisation and your serviceability will be top notch. Have a couple of monkeys in the repair organisation that break everything they touch, the opposite. The other thing you have is though some bits of kit may be built by the same firm, the design team developing and making those bits will be completely different, thus one bit to kit will be top notch, while the other will be a complete pile of poo.
As the experience levels of your staff gets higher, the more serviceable the kit gets, age of equipment does have an effect, however if the kit is set up correctly it should be less of an issue. By setting up correctly I mean measuring the output at the test point and if it's on the verge of being outside of tolerance, try to get the reading to the middle of the spec. If that cannot be done the item being serviced is on the way out and should be replaced (if you have the spares of course). Most of the real long term defects I've seen in 30 years of doing electronics have been because the last person to do the servicing didn't do that (the reading was in spec (just), so he moved on to the next step of the servicing).