Weird Tacho Problem

[JimX]

First the short version with integrated questions first to keep it simple.

Is the tacho needle sprung from around the middle of the RPM range (ie, around 5500 on the Nismo GTR version) so that if you move it up from this point, it will actually spring UP to the maximum? Somehow I doubt it. Would this be fixable at all or do I have to chuck and replace?

(henceforth the above description shall be referred to as the "spring thingie")

Now the long and complicated version with the numbered questions at the end.

About a week ago, the tacho stopped working. Well I thought it did. But then it worked again, of its own accord. This continued off and on for a few days, when it started to not work more often than work. Then one day it stuck on around 5500rpm, then on the same journey it jumped all the way up to 11000rpm and stayed there. What I'm guessing happened is I revved to around 5500rpm while it was still working, then suddenly the signal cut out, and when it finally jiggled loose, it was on the other side of the spring tension and hence jumped up to 11000rpm.

Last night I pulled the dash out and discovered the weird spring thingie I described above. I took the clear front off but left the tacho itself in the dash. I sprayed the **** out of it with contact cleaner, but it didn't seem to change the spring tension at all, it didn't feel like there was anything gumming it up so the cleaner wouldn't have really done anything.

I put it all back together and it surprisingly worked. The contacts from the loom weren't dirty but I cleaned them anyway to be sure. It dropped out and stayed on zero once, but within a minute or 2 it started working normally again and so far hasn't stopped working since. I'm guessing this isn't permanent though.

When it's working it seems absolutely fine, the redline is at 8000 and it seems to be accurate. The ECU doesn't do anything different whether or not the tacho is working, so it's got to be a problem with the signal between the ECU and the tacho, and the ECU obviously doesn't care what the tacho reads.

So now, my questions are:

1. If the spring thingie isn't normal, would it be fixable or would I need to replace the tacho?

2. How do I safely take it out of the dash cluster? It looked like the needle was in the way and I didn't want to break anything unless I knew it was stuffed.

3. If the spring thingie IS normal, I am guessing there is a loose signal wire from the ECU. How do I find and test it?

4. Where can I get a Nismo tacho from? I've only ever seen the speedo head units or the entire dash. Would a stock one work in the Nismo dash or would it read wrong?

That's all I can think of for now.