I used Shell Rotella T 15-40 diesel engine oil. Autozone stopped carrying Rotella T, but I got four gallons for $12 a gallon at Pep Boys - just a longer drive from my house.
I used Mobil 1 V-Twin Synthetic 20-50 in the Sportster last oil change. After reading about oil and considering the fact that Mobil 1 oil is about $11 a quart (after tax) and I need 3.6 quarts for the bike I decided it just wasn't worth the money. Harley recommends diesel oil - if you can't buy the special label HD oil (which I wouldn't do anyway), so I'm sure it will be fine.
I want to change the oil and filter on the Concours but I'm waiting for some more K&N filters to come from Amazon. I got a really good deal on 4 filters but they are out of stock right now and won't be in until early July. That's fine since I changed the oil and filter in March and could go another 2000 miles before I hit the manufacturer's recommended oil change interval (6000 miles for the Concours).
The Sportster manfacturer recommended oil change interval is 5000 miles and the KZP is 3000 miles (although somewhat oddly Kawasaki recommends only changing the filter every other oil change). Kinda like taking a bath with your dirty socks on to me.
There's a small oil drip on the left side of the Concours engine that I think is the clutch rod oil seal. It's an 8 dollar part and the installation sounds pretty simple. One of the really nice things about the Concours is they have a very good owners group who tend to do most maintenance themselves and share tips via their forum and group pages. An example is this article on the Clutch Rod Seal Replacement. It's good to know things like if I push the seal in too far it will fall into the engine and I'll have to go fishing and hope I can catch it with a magnet or a bent coat-hanger.
I have a clutch rod oil seal ordered from Cheap Cycle Parts for the Concours and a new Emgo (cheap at 8 bucks) air filter for the KZP. So that will give me something to do in a few days.
I've ridden a little over 13,000 miles on motorcycles since last August. 5K on the Connie, 5K on the Sportster and 3K on the KZP. I use the KZP for my wet weather commuting bike since it has a big windshield, fairing and is very rust resistant, the Sportster is for sunny days and fun rides around town and on short trips when I want to feel the wind in my face and the Connie works good for long trips - although I've yet to ride it in really hot weather (unfortunately).
Almost all my transportation is via motorcycle but I start up my 25 year old pickup every so often and take it for a spin just to keep the battery charged and evaporate the moisture from the crankcase. I changed the oil and filter on that a few weeks ago and used a mixture of Valvoline 10-40 motorcycle oil and Chevron 10-30 automotive oil that I had left over from some other oil changes.
My general rule of thumb these days is to change oil and filter every 6 months but if I'm going on longer trips I'll do it more often so I don't exceed the manufacturer's recommended miles between changes. I changed the oil in that pickup at 3 month/3000 mile intervals for over 20 years and put over 200K miles on it and that seemed to work. I'll test it for another 20 years using the 6 month intervals and see how that works out.