Assuming it's not setting or clogged video head related, it's likely to be capacitor issues. Panasonic had a preference for SMD capacitors on the video processing boards in their high-end machines, so it's highly likely they have gone bad and leaked.
I'd first try leaving a (known-good) tape running for an hour or so, as it may improve with use - also a quick 'n' easy method of 'cleaning' the heads should they be clogged..no I did not say quick 'n' lazy. Ahem!
Either way, I think you're still looking at some sort of repair or maintenance further down the line. Even ten years ago these machines were getting quite long in the tooth, and they do tend to go wrong even when sitting idle. Some say that lack of use can be a contributing factor with anything electro-mechanical in nature, but I digress..