I was told years ago that excessive downshifting to slow a vehicle is hard on the differential. I guess it puts a reverse load on the pinion bearings and/or gears, or something like that. But I've never had that confirmed from another source.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)