A quote from the Service Manual

"Models 116.120,123.133/153, 123.193 (usa model) and 126.129 are provided with an engnine mount without stop since start of series.

Model 123.193 standatd version has been provided with an engine mount with stop up to July 1981

Starting July 1981 likewise without stop.

for this purpose , vehicles with automatic transmission W 4 B 025 (722.120) had to be provided with a rubber buffer on transmission tunnel to prevent transmission vent form knocking against tunnel.

If a new engine mount with stop is installed, the stop requires adjustment after 1000-1500 km and 7500km

123.193 part number 234 242 04 23 with stop
123.133 part number 123 240 25 18 without stop
123.152 Same
123.193 Same
126.120 part 116 240 04 18"

With stop mean with the oval tube in the center.

So your 123.133 should not have the oval tube.

But it should last for a while.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car