In answer to your questions, the manual (as you have most likely read) states a 6000 km service interval after the first service that is, I do an in between oil change and keep the oil filter. The filter is changed on the 6000km service. The oil plug and crushable washer has never been changed as I only do it up tight enough not to come undone and it doesn't leak. As to type of oil to use, you can use a wide variety of brands just keep to the correct viscosity and dont use anything with friction modifiers as that plays havoc with the clutch which relies on friction. A lot of people with large bore single cylinder engines try the diesel oils I haven't tried those as yet and personally prefer the mineral based oils not the synthetics but that is personal choice. Apparently the oils with long chain polymers are not the best choice for engines with old fashioned ball bearing type bearings AKA KLRs as it gets broken down pretty quickly. I hope this helps and I am sure others will chip in with advice.