i have the b8200; it's about 30 years old and i've had it since 2014. the oil capacity is 4.1 qts, but it always shows full on the stick at about 3.5 qts. the stick appears to be the right one, ie, the original one. it doesn't appear to be defective or too long or any thing else weird. should i put all the oil in, stop when the stick shows full or what?