Found this write up on the oil change, thought it might be of use to new guy like me
I always did as KTM guru ‘KevInYorks’ said in that post; http://www.ktmforum.co.uk/technical-how-tos/20015-rfs-engine-oil-change.html
RFS Engine Oil Change
RFS - 4 stroke single cylinder 1999 to 2007. 250/400/450/520/525/540/570 The motor with two oil filters
250 miles, no need to change filters… do a quick change
With engine nice and hot after a ride
Loosen 8mm allen key headed short screen plug under motor. Use a good quality short 8mm allen key socket, hit it hard with a hammer to shock it then unscrew and catch oil. Check screen for bits of metal then clean off with carb cleaner, smear threads with copper grease and set aside.
Remove 13mm ring spanner magnetic drain plug from rear of motor and catch the oil. Check plug for bits stuck to it & wipe clean. Look out for the copper washer, it may come off with the plug or stay in the case recess.
Move bike vertical then tilt over to left to drain most of oil out.
Replace short screen plug, torque to 7 lbft which is just enough to nip the O ring
Replace magnetic plug and tighten firmly by hand. Watch out for the copper washer getting crossed up and not sitting into the recess, it must go in there otherwise the plug mag fall out!
Wipe clean around the plugs.
Put 1 litre of oil in.
Start motor for 30 secs.
Check for leaks.
When it has cooled down the level should be just on the bottom of the sight glass.
Every 4 oil changes, do the filters…
Turn off fuel, ideally turn off 500m before you get home to drain the float bowl a bit to minimise spilling petrol while bike is on its side.
Drain as above, then replace plugs.
Remove long screen plug near gear lever with a 13mm 6 pointed socket. Pull out the long screen and check for bits of metal then clean off with carb cleaner, smear threads with copper grease. Slide the long screen onto a long philips screwdriver and poke it through the hole at slightly below the horizontal so the end of the screwdriver goes into the hole where the screen goes, then side the screen home. refit the plug and tighten it to 11 lbft.
Lay bike on it’s right side.
Remove filter covers. A wobbly 8mm socket is ideal cos one fouls the sprocket guard.
Pull filters out of cavities with circlip pliers. Get ready with a container to put the filters straight in cos they are wet with oil.
Suck the dregs of oil out of the cavities with a syringe and tube if you are anal.
Smear the O rings with oil and put them back in the recess of the engine, not on the covers.
Half fill the rear (lower) cavity with oil and pop in the short filter. Replace cover and tighten screws to only 4 ftlb.
Do same for long filter.
Then put bike on stand and put in a litre of oil (not including the oil you have already put in the filters)
Wipe clean around the plugs.
Start motor for 30 secs.
Check for leaks.
Check level properly when cold.
NOTE:
They do not like having too much oil in them. Better to run just below the sight glass when cold than above it when hot
Oil change frequencies can be quite variable for RFS. Oil and filters every 1,000 miles seems to be the golden rule with oil only changes from 1 to 3 times in between, depending on use. I’ve always done mine every 300 or so miles (+ filters every 3rd change) and my bikes have been dead happy with that arrangement. But I know of a rider who’s used his 525 for green laning all year round for several years, never attempts any kind of maintenance himself but takes it in for a service every 12 months. Apparently when the oil is dropped it never yields more than about half a cupful of black sludge - and the bike has never missed a beat, just keeps going! Rather him than me though.
BTW I’ve never bothered with the sight glass - precisely a litre goes in with each change (1.2 on a filter change) and as long as nothing is being dropped and there is no obvious signs of leakage or oil being burned then I’m happy to leave it until the next change - which is never far away anyway. If you’ve completely drained out the old oil* and refilled with the correct amount then there’s nothing to check, no matter what the sight glass might be telling you ;)* after all the oil has drained out with the bike upright I tip the bike right over onto its left side - quite a lot more oil flows from the long screen cavity - then with the bike upright again I get the last of the dregs out with a syringe. Can’t remember if this has been mentioned in the above posts but remember to apply copperslip to the threads on the long and short screen plugs as well as the magnetic drain plug before torquing up - makes em easier to get out next time.
Which oil do people use?
Thats very important , no problems when comes to oil change again 
PUTOLINE OFFROAD 4+ 10W/60
http://www.putoline.com/en/products/catalogue/segp_offroad/p4tmo/592/off-road/four-stroke-motor-oils/ester-tech-off-road-4-10w60/
http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_221631_langId_-1_categoryId_165507 - word of warning: this oil is well hidden on the website - searches for fully synth oil just bring up car products
:)(I always get the cheapest fully synthetic bike oil I can find - 5W40 or 10W50 - previous batch I used came from Hein Gericke.)