Next to the baseplate, there was the machine itself - extremely dirty, a bronze-brown all-over. Fortunately the brown hue all-over the mechanism was a century's worth of dirt, not rust. Nevertheless it can be difficult to clean off - it is very greasy and hard.
The key-levers are easiest to take off the machine yet turn out to be the trickiest parts to clean. The key-tops are too fragile to be all taken off the levers, so the levers can't be cleaned in the soapy-water bath. The keys themselves need to be cleaned 'dry' anyways, because of their paper inserts. To start with, steel-wool is needed to remove the first layer of dirt, then metal-polish to shine-up the nickelled part and finally using aluminium-rubbing to mask any remaining spots of rust.
Although the key-levers take a lot of time, it's worthwhile and the difference is very noticeable.
One more thing; taking off the carriage-return lever is something perhaps best avoided. This is mounted with a very tricky hidden torsion spring mounted inside a chamber around its mounting screw. Re-mounting this is 'difficult'. (Am sure the factory must have had some sort of secret tool or fixture to accomplish this.)
The machine is taking shape again - and is now nickel-coloured :-)