There's actually not a lot that can go wrong with a Sedgwick, Unless you absolutely abuse the hell out of it they are pretty much bombproof.
Perhaps a close inspection of the tables to ensure there aren't any cracks anywhere (As Wallace said), most likely spot is the part of the table closest to the cutters. It's also worth checking along the table edge where the cutting happens for any chips out of it. It might be worth giving the feed rollers a rattle by hand to see if they've worn their housings but this rarely happens. Other than that there really isn't anything else other than your general wear and tear parts like bearings, belts, and the chain.
I went to go look at a Whitehead planer thicknesser 3 years ago which seemed great from the pictures but in person, you could see it had been abused with timber riddled with nails, massive scoring marks in the on the surfacing and thickness tables which weren't obvious in the photos, along the edge of the infeed table where the cutting happens there were these massive chips out of the table from where nails had been ripped out of the timber and got smashed into the table, on the outfeed table by the cutter block there was about a fist-sized chunk of cast iron cracked which could be moved by pushing it down with your finger, if that were to drop into the cutter block it would actually kill you. I promptly walked away from it, but I assume somebody bought it in the end.
Recently picked up a Multico 12" surface planer and a Multico 12" thicknesser, separate machines. I may have paid a little over the odds for them because machines of a certain calibre never come up for sale in this area. There's been a lot of TLC needed on them but they should last me a very long time now.