Adam
To go back to the origanal point of the thread, I have to agree with IO540 in the fact that not enough money has been spent on maintaning the aircraft you are flying for years.
The problem is that a lot of aircrafr have the King KR85 ADF fitted, in it's day it was a good unit but with out product support from King it is getting very hard to maintain these units and with the end of ADF not far away the £4000+ bill for fitting a reliable King KR87 ADF it is simply not worth doing.
I have found myself in this position as I have an aircraft with a KR85, A pole of my customers indicated that they would rather have an IFR GPS fitted at much the same cost.
The other aircraft that I rent out has a KR87 that works just fine by ADF standards.