hmm, well I really doubt the problem to be connected wit the locks themselves because u mentioned that they worked fine with another cluster.As fuses and grips are perfect, so here is no chance of a faulty connection as well.
And bro let me tell you something, they actually don't "change" EP ROM to tamper the mileage, they "reprogram" it. Thats what your guy did.
Now we have your issue rounded up that some diodes have been messed up with and hence are dead. As for the opening, I would strongly suggest NOT to open the cluster by yourself if you don't know what you're about to do.
Take it back to the guy and get it opened.
Now if you have idea about circuit repairing, give it a shot. Otherwise take it to a person who knows fiddling with miniature circuits. He'll be able to trace some circuit paths which are not operational and hence you'll be able to identify precisely which diodes are dead.
Get them fixed if possible, otherwise I think you'll have to replace the cluster itself or may be a small part of it, like the dead paths can be re-allocated to the board. Really have no idea what it'll cost though.
P.S. Can u post a picture of the cluster of at all possible? The grips plugged into it?
