Unfortunately the top fastener on my '88 is an allen head (10mm, I think) sunken into the fastener and the Official MB-Approved tool has a handle about 4 feet long (which the boys at the dealership like to crank on) so it is very hard to get loose.

I ended up completely removing the 13mm/19mm adjusting bolt on the bottom and was then just able to slip the replacement belt on...

Why do they do this kind of stuff? It is exactly the same situation with the a/c idler pully tension: they have this 4 foot long convoluted wrench and then tighten it so tight you have to use a hammer on a modified box end wrench to break it loose!

p.s. There is plenty of room for a conventional bolt for the top fastener.

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435