It's so tempting, when your machine is really dirty after a run, to attack it with a pressure washer.

In general, no harm in that. You might blow a bit of loose paint off, but there are other dangers in using high pressure washes.

Never direct the jet directly at these areas!

You can easily drive both water and grit particles past the rubber seals on the wheel bearings, leading to early failure.

The same applies, perhaps a lesser extent due to the positioning, to the brake calipers. The seals on the brake pistons again are not proof against high pressure.

The final drive unit has a pressure relief system built in. I have not checked this, but it seems reasonable that if there is a way for pressure to get out, then there probably is a way for pressure to get in!

The radiator has rather delicate finning, not made any more robust by being over 30 years old. You can and will cause damage by directing the jet at it.