Enjoy your new bike....
Wet crud in the spark plug well is probably oil which has leaked from the valve cover. Besides the big gasket around the valve cover, each spark plug hole has a small round gasket. This is assuming the spark plug was torqued properly in the first place (10 ft/lb). Be gentle with the valve cover bolts. (87 INCH/lb).
Make sure your spark plug socket is thin walled, otherwise it may not fit into the hole.
Oil: I've been using Mobil 1 Motorcycle oil, 10w-40. I personally wouldn't Do NOT use automotive oil. Some contain The additives for higher fuel mileage which may will cause clutch problems (slippage). It takes 3.2 qt. with a filter change if you pull both drain plugs. Some folks don't bother with the front drain because you only get a couple more ounces out of the engine. They just put in 3 qt. and they're good to go. You should be approx. half way up in the sight glass after the bike has sat for 20 minutes or so on the center stand.
Crank/Tranny: Shares oil from the engine.
Fork Oil: I switched to 15 wt. Belray and like the improvement. Your lucky, your '87 has drain screws at the trailing edge of each fork. Be sure to put a little liquid gasket on the threads and do not over tighten after draining the oil (13 INCH/lb). Be sure the front end is securely suspended off the ground and loosen the upper triple clamp bolts BEFORE trying to remove the fork cap. (Triple clamp bolt: 11.5 ft/lb, Fork caps: 16.5 ft/lb).
'86 - '93 fork oil capacity: Approximately 330 mL when changing the oil. After draining the forks and the springs removed, extend the fork tubes fully. Pour in the oil until it's close to 355 mm (13.97 inches) from the top of the tube. Pump the forks to get the air out then adjust the fluid a final time. A mm off high or low is OK, just as long as both forks are the same. You can do this with the forks on the bike.
Coolant: I've be using Preston Extend Life. It is "silicate free". That's the important thing. Get a gallon of distill water to mix a 50/50 mixture. One gallon of the 50/50 mix will fill the system (3.1L) and reservoir. The drain plug is in the metal coolant tube under the belly pan. Be careful with the drain plug, also (69 INCH/lb). My radiator filled easier with the bike on the side stand. Once filled, run until hot and the thermostat opens. Let it cool and top everything off. There' a bleed valve on the thermostat housing but I've never had to use mine. Also, the manuals say you have to remove the carbs to get the thermostat out but if you're patient, you can get the thermostat cover bolts out and wiggle the thermostat cover out towards the front of the bike. Be sure to replace the o-ring, too. You don't have to buy a $35 Maw Kaw thermostat. Do google search on "Kawasaki Concours common part numbers". The o-ring size is also listed. I got several from "theoringstore.com"
Brake fluid: Standard Dot 4 Brakes are good for about 2 -3 years but the clutch needs to be bled about every 6 - 8 months or when the fluid begins to look murky.
Final drive: GL-5 hypoid gear oil (80 wt. for below 40 degrees and 90 wt. above), about 220 mL or until it starts to overflow from the big cap with the bike on the center stand.
Rear wheel splines: Keep the rear wheel drive splines greased as well as the mating splines of the final drive. Use a moly grease but not too much. Honda has a Moly 60 grease which is much better than the stuff you get from the parts store but the other stuff will work OK. The splines need to be checked about every 6K miles or more ofter if you ride in the rain or dusty conditions.
Suspension linkage: Grease the torque arm fittings.
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Good luck
