I personally wouldn't do anything until it showed some signs of a problem. The great advantage of the 119 wiring harness problem is that you don't have to touch it - either to do a head gasket or to change the plugs. I can understand why a shop wouldn't want to go near it but the likelyhood of it going from good running condition to fire without any operating warning signs is pretty slim. The problem with getting ahead of the curve with preventative work on these cars is that their eroded market values leaves very susceptible to being totaled at any time from a relatively minor fender bender. But it is only about $500 if you shop around and a couple of DIY hours to install - personal choice.