Wow!... I'm a bit at a loss of what to say here. Never ran across a locked up X yet. again, Wow.
so, have you verified that it is truly locked up. for example, did you get it off the ground, pull the spark plugs, put in 5th gear, and try to spin it? Please ask me if you don't know how to get the spark plug boots off, but I'm taking for granted, since you got the relays replaced, you know your way around. ....
And for my benefit, ... you pull clutch in, it rolls? .... and/or netrual? just trying to make sure the tranny isn't locked up, with motor included.
If this, or what ever you came up with verifies that the motor is locked up. My resource to contact would be Jamie at Atlantic EH.... only because I've done a lot of business with him. He maybe hard to get to the phone, as he is busy, plus some personal issues going on the home front. He has helped me out a lot, when I got cornered, and will give you his time, when he has some, with pleasure...
I'm sure, he is using an aftermarket piston on rebuilds... he'd know where/howmuch/when. If not set you up with his own stock....
And being I don't know for sure, but I'd guess strongly the other vendors listed on this site, would also have their own sources....
curious, as the cause of all this.
X's are notorious pukers, until the engine is fine with the level it wants. I did have a bad puking problem a few years back, due to the fact that both oil pumps were scored, and pumping air pressure into the engine case. Took a bit to figure it out, but it didn't lock up.....
lemme know what you find out.... got my mind a thinking... and good luck....