I do not even find that partnr for the 99 SL500,
but browse here to find the parts for the
different models (should be group 80 for all);

http://www.detali.ru/cat/oem_mb0.asp?TP=1

Most of the models list the lock as 1298000874.

br,
syljua

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1998 CL500 W140
1984 230E W123