Is there anything on this topic anywhere?

The description suggests that weapons shouldn't really be able to jam anymore. However, it doesn't actually say whether the weapon can or cannot jam.

This became relevant in a game just now, where a player chose to take Slayer Limb with a Plasma Pistol. Clearly, it's a really good pick, but at the same time, what happens when it Jams? Plasma Weapons don't jam, they Overheat instead, but if it's a Slayer Limb, it can't get dropped.

On one hand, I'd be delighted to see the arm of the heretic blown off by his hubris. On the other hand, it seems like a bit of an oversight.

What gives?

As you rightly pointed out the rules dont say it explicitly but the description does suggest it. One thing I noticed which might support your argument is the line:

"...and henceforth never requires reloading or any other type of maintenance."

That to me may include reloading, repairing and unjamming of it. Effectively it's almost like a tyranid bio-weapon and last I checked they don't really jam up all that often so I would agree to not allow jamming. The mechanism is effectively part of your body on that so your body almost controls it and makes it fire.

Overheating though I would allow. It might be fused but it can still get really warm from use or bad luck. No amount of bio circuitry or integration stops plasma firing from a metal gun barrel from transferring heat to said gun and since it's attached, the heretic can't drop it short of quickly hacking off their own arm. I would believe this to a balanced reward. The gods grant the heretic the right to always bear a weapon with all the benefits of no reload/ammo etc but must always run the risk of any such item overheating/overloading and suffering the consequences. The fickle nature of Chaos and all that.

It's immune to any ammo related issues, including jamming. Overheating isn't a ammo or maintenance issue, per se. Either you have slayer limb not being able to overheat, or just only use it with BC overheating weapons.