boom suddenly will not raise

Hey guys, I've lurked here for a long time and learned a lot. I've got a question I hope someone has some ideas on as it's driving me nuts.

I have an older (1998) Versalift bucket truck - an old AT&T vehicle. One morning, I went to raise the boom and there was a 5 second delay or so before it began to raise normally. I lowered the boom and the problem went away for several raise-lower cycles. Then the boom would no longer raise at all.

The hydraulic system is pretty basic. There is a...

boom suddenly will not raise

boom suddenly will not raise