I have done this job on my X. The coil I bought was also from ebay. It did come with a seperate diode that I would have had to put in-line but I did not use it. I have had mine in for about 5K miles now and not problems w/o the diode. The system works exactly as it should.

As far as indexing is concerned, I don't remember aligning the replacement coil with any special tab. Only remember making sure the wire exists up top so that it does not interfere with the spinning pulley. The snap ring will hold the coil very securely. I did have to grind down one spot on the replacement coil where a pin protruded out the front of the coil that would have made contact with the pulley (maybe an alignment pin for a different application).

There is a good write up on here with pics that I followed. The only difference is I had a heck of a time getting to the snap ring so I ended up cracking open the system so I could work with the compressor in hand.

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2010 Lexus RX350 still new
2003 BMW X5 3.0i w/sport package w/68K miles. (gone Thank God!)
2002 Dodge Ram 2500 4X4 cummins diesel w/198K miles, custom repo truck
2009 Scion tC w/46K miles
2007 Suzuki SV650 custom streetfighter
2000 Lexus GS400 w/165K miles