The M110 inline-six 280SLC is prized for its smoothness and ease of work but is widely called slow, especially with the automatic; a manual sharpens it. Manual 280SLCs are genuinely rare, and sourcing the 4- or 5-speed manual to swap is difficult and expensive (a UK kit is cited around 10,000 pounds).
280SLC inline-six and the rare manual variants
Mercedes-Benz SLC (C107) · mechanical