well, depending on your luck I guess, some people say distributor, but mine is still healthy after 120,000kms. But mostly people say it's the distributor
My list of parts changed since my conversion to B16A,
4 Sets of tires, total of 8pcs, RT-215, now on RE001 205/50/15
S2 Valvetrain (valves worn out in piston one, suspected due to improper valve lash)
Clutch pad,
Bushes, all front end.
A/C compressor = 2nd unit replaced (mampos-ed, constant high rev = bad for AC?)
A/C hoses (leaked)
Brake pads (worn out the prev. set, now on endless NA pads
Apart from that, everything still works, in terms of the engine.
If you feel it heavy, it's probably because I do a minimum of 120km mileage per day... that's the least, anyway.
Monthly, it exceeds 5000km, that's for sure.
You have to budget repairs into your 2nd hand car, most people don't really maintain their engines, but rather fix things in a way that goes "as long as it can move", and when they feel that they've had enough, they sell to others.
So make sure you have at least 2-3K free after purchase for repairs, timing belt, rubber seals, hoses, etc. might need replacement.
2-3K is conservative though, because if you have the gearbox konk out on you (if you bought a high mileage ride), it will go over that amount very easily.