The part number is 110 683 00 10. Two are used on the 230SL and 250SL up to chassis number 004189. They are not applicable to later 250SLs or any 280SLs. I believe the covers are still available. MB USA list is $20.00 and my price is $14.77. Each cover is retained by two little clips. These are part number 001 988 44 78, MB USA list $1.70 each, my price $1.23 each. The clips appear to be available although it was not too many years ago that there was no stock.
Ah, the very sticky subject of subframe covers... I agree (mostly) with what Dave says and will add a little. For quite some time subframe mount covers have sold on ebay for more than MB charges for the same part new. I have new ones on my 250 SL and I have old ones that I have sold on ebay. I have complained about this in the past (selling for more than available new) when other sellers have done it and in discussing this with the other sellers the argument has been that "these are old and slightly different from the new ones that MB is making now". That may well be true. They do indeed "feel" a little different than the new ones. I am also guilty of selling old ones for more than MB charges for new ones, again based on what others say. Given that, just be aware that you can get them new or you can get them used and you decide which you want. (my used ones appear as ebay item 150399361877 if you are interested in pay more than new price, and I'll do 15% off my ebay price on anything I have listed - see my post in Commercial Listing for info).
Regarding the clips, they are available new, but MB says to use 3 not 2 per cover (I ordered 6 for an ebay buyer in October 2009 and then the buyer flaked). I agree with Dave's part number for both covers and clips. There is not a different part number for "old" vs "new" covers.
