I have a Deere 250 skid steer (1979) that won't raise the boom. The bucket flips up and down great, it moves forward and

Customer: I have a John Deere 250 skid steer (1979) that won't raise the boom. The bucket flips up and down great, it moves forward and backwards good. The boom will not raise at all. I raised the boom with no problem. It was left raised for about 5 months (I was in quarantine by the Covid-virus) and when I got to lower the boom, it came down without a noticeable problem. However when I tried to raise the boom it would not go up. It seemed like one side (right) was lacking in hydraulic power. The left side acted like it it was trying to raise but only slamming to the right laterally a few inches not up. Depressing the foot control to raise the boom would only slam it back to the right. I don't understand the reason for this erratic action. There are no leaks in the hydraulic system that I can find. My manuals (parts, technical and operators) don't address such behavior. There is a mention of " boom lock", "boom spool", "port lock" and selenoids. Since I am not knowledgable in hydraulics these items do not explain the reason for their use. Could any of these items cause such a problem? I would appreciate any information that would help me get my machine going good again.
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Heavy Equipment Mechanic I'm going to connect you with knows all the tricks and shortcuts.
Customer: How do I get connected with such a person?
JA: Anything else you want the Agriculture Mechanic to know before I connect you?
Customer: I would like to repair this machine myself in order to learn more about these types I problems. I am 91 years old and only use this skid steer around the home, no outside work at all.