Kind of hard to tell, I am guessing 25 to 30 cm. Hose diameter would best be measured directly by the size of the attachment point, 8mm?? The part number for the rear connection from the heat exchanger to the oil filter canister is 127 180 01 27. The longer pipe from the front of the oil heat exchanger to the oil filter canister is 127 180 03 27. Unfortunately the part book does not have the hose size listed or shown.
If you have the small parts book (12128) for the 250 SL, the oil cooler is shown on Table 10 and parts 86 and 87 are the oil lines I typed about.
I looked at the 230 SL parts book and the oil cooler is there, but the configuration for the solid lines to the oil filter are different. The smaller connector appears to be the same.