I spent a LOT of time getting mine working. You can spend a crap ton of money and buy all new bits, but I didn't.
On mine, I have a manifold that has a bunch of one way metering ports. Some are differents sizes for different flows of oil. I took everything apart, cleaned them in solvent and an ultrasonic cleaner. Sprayed the lines with brake cleaner and compressed air until everything was clear. I then hooked it all back together on the bench and ran oil in it until I saw it come out of each line.
The truth is, if you want to be sure it's working right, you HAVE to put in the sweat equity or spend a bunch of money on replacement parts, or spend a bunch of money and have someone else do it, or spend a bunch of money on a new machine. For me, I do not have buckets of hundos, so I don't mind putting in the work. I'm a hobbyist and don't need the machine to make money, so if it takes me a year (I think it DID take me that long to refurbish the whole machine) I'll spend the money only where I need to spend it.