Bought a new road bike last September, and the Ultegra rear mech has seized at the pivot where the cage joins the mech. In trying to free it off, I have rounded the allen key bolt that fixes the pivot to the cage (it’s still fixed, and I have worked it loose with lashings of WD40 and oil). Do you think it is reasonable to go for a warranty replacement, given that I have now damaged the mech?

good luck with that claim.

Why fail?

Yr only possible argument IMO is that they should’ve greased better on assembly

drill it off, buy a new bolt – maybe ask shop to do this for you, you might just get that for free

what maintenance have you done since September to keep all pivots from seizing?

Have you kept the mech clean and lubed? Did you ride it through Winter?

It’s a rear mech, what maintenance is required? Nothing in the manual about regular oiling of pivots.
Never pressure washed, not used through the salty winter.

My XT mech on my commuter has seen 10,000 miles of use over 4 years and not needed any attention.

It’s a rear mech, what maintenance is required?

Stuff like this.

Three Fish,
that’s been done – it’s all been kept clean, the parallelogram pivots have been oiled, the jockeys cleaned and oiled – they are all fine and as new. The pivot that has seized is the one that joins the cage to the derailleur body, and keeps the chain taught; the one with the spring in that “should” be packed with grease. I haven’t been able to get in there to see of any grease is required, but I would expect a bit of grease on £70 worth of rear mech.

The pivot that has seized is the one that joins the cage to the derailleur body, and keeps the chain taught

ah, sorry – I thought you meant the mounting bolt

I serviced a mate’s commuter once – road kack had set front and rear mechs completely solid and they had to sit in plusgas overnight to dissolve it and start to move at all