hello Mauro, the 'sockets' on our W113 bulb holders are also used on W107s, W108s and several others. I think the easiest and most reliable fix for this problem would be to replace the positive (+) lead with one from another bulb holder. Attached is a photo of a positive lead from a W107 bulb holder and you can see its identical to the broken one on your bulb holder. You'd just need to solder/splice the new pos (+) lead. W107 bulb holders can be found on eBay and are fairly inexpensive.
I replaced a cracked bulb socket on my 230sl just this past weekend. I bought a w107 bulb holder on eBay for $25 USD and since there's 3 bulb "sockets" on a W107 bulb holder, I now have 2 extra sockets and positive (+) leads. If you weren't so far away I'd send you one (it would probably take a month for you to get it!).
If necessary, old bulb sockets can be drilled-out and replaced with sockets from w107s, w108s.
