how hard is a valve stem seals job.on a 2.4 liters nissan.
It’s in the moderate range IMHO. You’re going to need a few specialty tools along with an air compressor or by using one of several trick methods to keep the valves from falling into the cylinders.
If a valve drops in then you’ll have to remove the cylinder head so if you’re not mechanically inclined I would not advise DIY.
The answer depends entirely on your skills. I tend to say though- “If you have to ask, it’s probably over your head.”