As an electronics engineer that works on semiconductor manufacturing equipment when you say it sometimes corrects itself when you swivel the base it sure sounds like a connection problem. I'd start with all your input connection as since you have a swivel base these would be the logical place to look at first since most connection inside won't be subject to the turning force when swiveling the base. Since you've been in the TV before maybe something you had to disconnect to replace the boards has come loose.
Another thing you should do is look for the service manual. In my Panasonic service manual it has a troubleshooting section that has pictures of different problems. That should narrow you problem down and keep from spending money on boards not needed.
As far a price, are the parts available at a reasonable price? If the board you may need is super pricey ($100+) If it were me I'd just start shopping for a new TV.
I was in the same boat. My Panasonic TH-42PX50u died all of a sudden, similar picture problem that you are describing but all the way across the screen. I went ahead a bought a Sony A8G OLED and love it. All the problems you hear about with OLED I don't seem to have (motion, image retention etc). I've had it for almost 6 months now and love it. I couldn't just let my old plasma go out to pasture so I started looking at fixing it. $34 later and it works great. At first I thought it was the main board and got one off of flea-bay for $10. That wasn't the problem but it did get me a little further as it posted a error code that wasn't posted before. It turned out to be the SC (vertical scan board) that I got off of flea-bay for $24.
If parts are cheap and you can find the service manual I'd say fix it. I'm still impressed with my 2005 1080i plasma picture even to this day. I would have bought another new plasma but the industry stupidly moved away from that tech. What a shame.
Sony 2019 Sony XBR-55A8G
Panasonic TH-42PX50U - 49,203 hours! DIED :-( then resurrected by me on 1/16/2020!!!!!
Various "cheap" TV's in kids room and video game room.