You should not have any problems finding parts. The engine is an M110, same one that came with the US 280SE and 280E.
It is hard to see how the dipstick tube would leak if the top end is properly secured. The sump gasket is also unlikely, but could have a loose bolt.
But I would suggest looking at the chain tensioner which is on the right side of the head behind the AC compressor and bracket.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe