Because of the position of the ignition hole on the 450, 451 and Roadster, it's very common
for them to get full of shit like dust, cake, sugar, fur, crumbs, bogies, chocolate, finger nails etc.
The ignition barrel isn't open underneath so anything that falls in, stays in.
Eventually it can stop the key going in all the way or it'll interfere with the mechanism.
If the key isn't all the way in or the pins/discs don't line up, the key won't turn.
If the key don't turn, you ain't goin' anywhere.
The 450 and Roadster use standard pin tumbler cylinders.
The 451 and 453 uses centre disc cylinders. The keys are often called Laser keys or Sidewinder keys.
The 450 and Roadster suffer more because of the cylinder design.
Get your vacuum, fit the nozzle and start vacuuming the ignition hole. This will help pull out loose stuff.
If you have a compressor and air duster, go for it. If not, you can buy cans of air duster.
The cans are very good as they tend to have a straw that can be put into the hole.
Once you have done this, try vacuuming it again to remove anything you have dislodged.
Don't be tempted to use WD40 or any other wet lubricant. You need a dry lubricant such as graphite powder.
Puff some into the hole.
This shit gets everwhere.
Put the key in and out of the ignition a bunch of times to help distribute the graphite lube.
Place the key into the ignition...