He sounds like he's been through a load in his lifetime and it's testament to good piggie care that he's still rumbling on and tutting at the New Pigs on the Block.
I know GP2 was prone to pooh issues , though he was younger , but I gagged when I had to 'assist' .
And when our GP6 was ill (over New Year a couple of years back - see their sense of timing is so bad ) we had to keep bum dipping him to stop his poor skin getting sore . He kept recovering , but eventually got to the stage we had to say " the end".
The last few days caring an ill pig is tough. You feel like you're bothering them but you don't want to leave them.
It's the feeding every couple of hours in the middle of the night with a little rodent , trying to convince them that you're doing it for their own good ..
Have you got Vit C ? Some of that in their water helps . Our GP6 in his last day (when I honestly thought he'd die in his sleep) developed a weird sort of bunny hop rolling movement . He still wanted to move , unreasonable little animal. We were making soft fleece nests for him and food beside him.
I think by then he was Vit C depleted and onto signs of scurvy . !
I cuddled him for about eight hours , he peed on me once and my God it smelled !
Our vet suggested an infusion and painkillers but by then we knew we couldn't prolong him.
Keep eating twinpigOldBoar (I;m guessing the "twinpigs" are your little baby pigs that you were hand rearing IIRC)