They were once smooth, though the newest 123 I've ever driven was more than 20 years old. Your hard shifting is vacuum related. Vacuum controls shift quatily on these old MBs. No vac hard shifts, too much vac causes flaring. Flaring is also a sign of worn internals. Start troubleshooting the vac system. You've either got a leak somewhere, or the vac control valve on the IP is acting up and needs to be replaced or adjusted.

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