It is becoming increasingly rare to find an LS with original black pipes/mufflers - the originals are-unfortunately- even MORE prone to rusting and corrosion than the chromed BMW ones. On the plus side, they can be easily made to look newish with a but of sanding and some hi-temp flat black paint, but once rusted through, you gotta find an alternative.
MAC exhaust used to sell a black ceramic coated exhaust set that was 2-1 and which fit the LS. They claimed no jetting changes were require but I suspect some tweaking may be in order with them. They don't seem to sell this anymore, but do have chrome sets, and you also have options from EMGO or BUB also. Like Steve said, if you're planning to enter it in concours show competition, it wouldn't fly with non OEM pipes & mufflers, but if you're going to ride it, a good stainless exhaust system is a good investment and many of these bikes on the street now wear shiny pipes.
Does the clutch "slip" seem to occur when you are driving on level/flat roads or going downhill?