yes it has a liquid gasket seal. You will need the correct liquid gasket sealant for reassembly, do not improvise! I use threebond stiff, #1104 I think but there are several others available that work well. Silicon and permatex are not good choices.
You just remove all the nuts and bolts holding the cases together and pry them apart. Quite a few pieces have to come off first, anything that goes between the cases - like the oil pump and shifting forks assembly for example.
Have the engine upside down and lift the bottom case off, the other way up is not good.
You can then lift out the transmission shafts and thread the primary shaft through the chain to lift the crankshaft out, then you can remove the main bearing shells. Then you remove the gear fork drive pins (a small magnet is useful here) and then slide the shift drum out the side, freeing the forks. A few other odd bits and presto! you have a bare case ready for whatever devilry you have in mind.
Get an oil seal kit and replace them on reassembly. Visually inspect the main bearings and consider plastigauging them, if worn this is the time to replace them. Look at the gears and think about replacing any with rounded corners on the dogs. Check the forks for bad wear where they engage the gears. Look for worn out grooves on the shift drum. Check the slack in the primary chain. If there's a slider block for this chain, replace it if it's badly worn down (not sure if the 550 has this). It's a good idea to replace the primary drive rubber blocks after 30+ years but they cost a few bucks. Check that the starter clutch is OK - the 3 each rollers, springs, and spring caps should all be in perfect condition.
There's a bunch of other stuff you can check and fix-if-bad. getting the engine open is a lot of work for a home mechanic and personally I tend to do as much as I can afford when I have one open.
