A multi-point lock only works if every bolt lands where it was aimed
This is the difference between a latch and a multi-point system. A single latch tolerates a door that has moved a millimetre or two: it is a wedge, and it will still find its hole. A multi-point lock has two, three or five bolts driven by one gearbox, and every one of them has to arrive in a small keeper at the same time. Nothing is forgiving. A door that has sagged by two millimetres drops the top bolt below its keeper, and the handle then fights you at exactly the moment the mechanism is doing its most work.
Which is why the first test is not about lubrication at all. Open the door and press the handle. With the frame out of the picture, anything that still feels stiff must be inside the lock or its linkage — the gearbox, the guide rails, the connecting rods. If the bolts shoot out and retract briskly and evenly, the lock is fine, the fault is alignment, and no amount of oil will help. This single test divides the whole page in half and takes ten seconds.
Why oil is the fastest way to make it worse
Oil stays wet. A wet surface collects every particle of dust, grit and metal swarf that passes it, and inside a lock body there is nowhere for that mixture to go. Over a season it becomes an abrasive paste packed around the pins, springs and gear teeth. The lock does not get smoother — it gets stiff, then gritty, then seized. The same applies to general-purpose penetrating sprays used as a lubricant: excellent for freeing a rusted bolt, wrong for a mechanism you want to keep working.
What works is a dry film. Powdered graphite, scraped from a pencil in a pinch, works down into tight pin stacks without leaving anything sticky behind. A PTFE spray that dries to a slick film suits the bolts, the connecting rods and the keeper contact. Use very little — one short burst or a small puff. Excess runs out, stains the door face, transfers to hands and then collects more dust, which is the opposite of the point.
Alignment: hinges first, strike plate last
Two millimetres of sag is enough to put the top bolt under its keeper, so the order matters. Tighten every hinge screw first. Then, if that is not enough, replace the two short screws in the top hinge with screws about 75 mm long that pass through the frame and bite into the stud behind it. The top hinge carries most of the door's weight, and factory screws are often just long enough to grip the thin frame — which is exactly why the door slowly drops. Longer screws pull the leaf back up and re-centre the bolts on their own. Only if lifting the door still does not align the bolts do you touch the strike plate, and then only by a millimetre or two.