I have 120 K miles and have started to get codes. Having had a Rabbit, I was thinking of threading the glow plug and using a ring crimp on. I got so far as threading an old GP, but did not like the threads that I was able to make, and thought that the nuts were too easy to strip off.
The post on the Glow Plug seems to be Stainless Steel, I tried solder, but it would not take. The Harness connector is some sort of spring metal, and when it gets hot with the 15 amps or so, it is going to corrode and not be a spring much longer.
I came across a wire nut with pigtail about a foot long. This sent me back to the Treading idea. The post is smooth, and the wire nut will not grip it as such. But what would happen if it were threaded? Then the wire nut should grab that post very nicely. A short length of the pigtail, and a spayed crip on, and you should be all set. The glow plug should last for about 100K miles.
Threading the post, and using more than one nut. Lock washers between them should give a little more tension on the lug.
Problem as I see it. That post is Stainless Steel. Were I work we use this for the hardware, Why? it does not rust. We also use aluminium, why? again, it does not rust. But you put Aluminium against Steel, and you have all sorts of problems!!! Like connectors on Glow Plugs!!! To stop this we have been using Di electric paste for some time now.
The Mag Wheel on the Axle trick. Took 2 1/2 hrs for AAA to show up!!
Have also been thinking of tying the leads together.
Permatex Battery Post protector kept my CEL off for about 40K miles. Then I had a GP fail, and changed them all as a set.
Best test that I have seen to check a GP is to put a Battery Charger on them, and read the currents. Do it Quickly in about 1 second they are going to Glow Red!