I used the bulbs from that kit on my 123 and later had a problem with heat melting the clear plastic that "conducts" the light to the front of the panel. Before you put in the new bulbs try another fix. Remove the panel completely (by the way 81Wagon is right, the oil line won't leak more than a drop unless you have pressure). You'll need to remove the speedo cable, oil line, and electrical connector at the back of the panel to get it free. You can access them by pulling the instrument panel out as far as you can and slipping your hand in behind. Do the oil line last. Once off you can easily get at the rheostat to solder a jumper or clean it up so it works better. The best fix is to remove the left and right instrument clusters (tach on one side, gauge set on the other) so you can get at the little "compartments" behind the two bulbs that light the whole panel. I found mine had both turned brown (they are supposed to be white) and painted them glossy white. This made a BIG difference. While you are at it replace the stock bulbs with new ones since those somehow get darker too. Chances are good this will solve your problem. I can't tell for sure that the "upgrade" blue bulbs caused my melting problem but I can tell you that after installing them the light was better at first but then got much worse. I eventually had to buy a new(used) cluster and applied the above fix. Since then the light is much better but still not as good as on my 124. I think MBZ improved this design in later models.

Old Deis,
Not sure about all the 123s but my '85 has the oil line to the gauge. It must be that some were electric and some mechanical.
Go figure.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold