[Yetiman]

My limited experience...

My first 6al failed in the first few weeks and was replaced immediately by the shop I bought it from. It seems the rev limiter circuit had developed a mind of it's own and wouldn't let the car rev over 2300 rpm.

I had installed the first one in the engine compartment on top of the passenger foot box.

When I got the second one, I mounted it inside using the same mounting holes, adding a hole and gromet for the wiring to pass through.

This one left me stranded, and when I returned it to the shop where I bought it they tested it and it worked perfectly.
I then ordered a Crane Hi6 based on recomendations on this site and because it has diagnostic modes and will try and tell you what failed.

Before it arrived I diagnosed the REAL cause of the problem to a faulty alternator wire.

I am still running the Crane box and in nearly two years not a hiccup.

Would I do it again ? Yes.

The car has better drivability and mid range response with the MSD box (noticably better than the Crane box too !).
I also got measurably better fuel milage with it too which I have never really heard anyone else claim.
Also, the REAL reason I bought it was the rev limiter, and I want to keep that.

I kept the Crane box in place because it has an input to retard timing with my nitrouse system which allows safer operation. I am probably going to remove the nitrouse this year as I never really use it, and will go back to the MSD 6al at that time.

Many problems where people initially blame the MSD box (including me myself and I) are actually caused by other electrical issues. The people at MSD and the shop I bought mine from told me this, and in the second case they were right.