The draught may not be the seal.
If a worn hinge lets the sash sit away from the frame, changing the rubber alone will not restore proper compression. Alignment and hinge condition need checked together.
Hinges, handles, locking mechanisms, seals, draughts and alignment faults can often be repaired without replacing a sound uPVC window frame.

If a worn hinge lets the sash sit away from the frame, changing the rubber alone will not restore proper compression. Alignment and hinge condition need checked together.
A stiff handle can be the symptom of a mechanism or alignment fault. Continuing to force it can turn a smaller repair into a broken gearbox or handle.
Tell us whether it is stiff, draughty, loose, jammed or failing to lock and we can start narrowing down the cause.