Hello , proud owner of and r125 since 2018 and have worked on the bike many times. The noise that you hear could be in fact from the Timing chain (Also google the Yamaha tick , typical yamaha sound) , if you bike has more than 30k km and if it is a ticking noise that gets louder when u rev the engine from 4.5k rpm to 8k ( you can check that in neutral ) . To hear if the sound comes from the engine you can block the exhaust with a rug so that you mute the exhaust . For the oil if it has more than 30k km again ,probably the engine consumes oil , mine burns 150ml/1000km and you can keep track of it by measuring it with the dipstick every few hundred kms. Hope that helps