Engine rebuild or engine change? big dilemma....

[Elwe2k]

So I went to the shop to get a CEL scan from a P0301 misfiring code on a possible bad injector. Last time I went to the shop with the CEL on was for the same code, mechanic decided to switch injectors 1 & 2 to see if it was the cause of the problem. Yesterday the CEL showed up again, went to the shop and the man told me that there are 2 possible reasons for that misfire code: 1) injector is indeed toasted or 2) valve stem seals are worn on that cylinder and they have to be replaced.

Overall it's not a biggie, you replace the seals, clean the cylinder head and off you go... but since my car has 225k+ miles on the clock it may be a good time to do a rebuild. So, here's the dilemma that's been nagging me right now: is an engine rebuild necessary since the head is going to be removed? I've read that misfires can be caused by worn piston rings as well, but in my case that's not likely (I think), car runs fine at the moment, rough idle is the only concern. I have replaced some parts like fuel pump and filter assembly, camshaft and crankshaft sensors, PCV valve, spark plugs (Bosch Iridium ones), ran a vacuum test with no sign of leaks and checked ignition coils which are OK. There's some oil loss as well, no leaks whatsoever. Maybe those worn valve stem seals are causing that.

What do you guys think? replace the valve seals only or go thru a complete engine rebuild? I was thinking on swapping to a newer 1NZ from late Yaris models too, but I guess those are a bit expensive at the moment, and that's not including labor and some parts.

Speaking of labor and costs... Shop is charging me $1400 bucks, parts & labor with 1-year warranty.... Funny thing is the car was $1200 when I bought it

Thanks in advance for your opinions.