Front seat belt inertia reel sticks in hot weather

Since I've had my Fabia Mk2 I've found that, especially in the summer, the inertia reel on the drivers seat belt tends to get stuck when it's very warm.

This often means that (even if I pull it very very slowly and gently), it will "lock" as if it's been jerked sharply. Generally speaking, though, when it's cold, I don't have the same problem. If i jiggle it repeatedly, eventually it will free up and I can put it on as usual.

From what I can see from the Haynes Manual, it's not that difficult to get access to it and, from another thread I've read on here, it's probably just that the works have got a bit gummed up over the years and some cleaning spray and new lubrication should sort it out.

My issue, though, is that Haynes says to "Disconnect the Battery Negative" before trying to do anything like this, presumably because of the "explosive" tensioner mechanism. But it also says that the ECU will lose its "learned" settings and the radio will security lock until I put in a code (which was probably lost by a previous owner long ago!)

So is it actually necessary to disconnect the negative terminal if I'm not going to be disassembling the mechanism? Is it just Haynes being overly cautious?

Advice would be welcomed.