You have a couple of choices here, neither of which includes you cleaning these yourself. You do not have the equipment or chemicals to correctly or efficiently clean and flow test these injectors. It is important to ensure each of the injectors flows the same amount of fuel in a given time at a specified fuel pressure. Only a professional service can provide this for you. You cannot just spray your injectors with carb cleaner and expect them to be clean and work correctly.
This leaves you one of two options:
First, you can replace your injectors with new ones, or for a better price (approximately half), you can purchase rebuilt ones.
Secondly, you can have yours sent out for rebuild. In doing so, the rebuilders will clean yours (probably with an ultrasonic cleaning machine, something like what is used to clean jewelry, but with chemicals to clean the injectors correctly and safely), replace any worn parts, check the electrics (solenoids, connections), and flow test them to ensure each is flowing the correct amount and the spray patterns look good. This process is a little cheaper than buying rebuilt ones, but you have the time factor involved in shipping and down time of your vehicle.
You made mention of your o-rings looking good. If these are the original o-rings, I can almost guarantee you they need to be replaced. While there might not be any visual damage to the o-rings, they do harden over time and conform to the hole which they have been stuck in for all those many miles. If they are left alone, they will provide many, many miles of worthy service. Once they are dislodged from their holes, trying to put them back is not only difficult, it will almost assuredly allow for leakage of air past them, exacerbating your lean condition. New o-rings are cheap. If the o-rings are original, they need replaced. Ensure you put fresh oil opinion them to help in insertion and to help guard against damage during installation.
Equal flow is important to the injectors. If they do not flow equally, you might have lean conditions in one cylinder while having a rich condition in another. This will create a power imbalance in your engine which creates more wear and tear. Your engine will last much longer if it is functioning correctly, as well as it will run much smoother all the while.