No need to purchase that tool. I used a 1/4 inch drive U-joint wrapped with electrical tape which allowed you to get at it at the proper angle. One of the most difficult fastener to remove is the top allen fastener where ther is only an inch and a half clearence. The tool wanted to "walk" out of the fastener head. I enventually got it buy using an allen socket held into the fastener head with much tensionwith a large screw driver and turning the exposed part of the allen socket with a box wrench. Good luck working space is limited.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T