I mostly have just used WD40 and the really thick bristle nylon brush and sometimes a plastic scrapper or a wood ice cream stick.
A brass wire brush if you have the room to use the brush.
If you can find a thick bristle brush without the cleaning fluid connector it should be cheaper.
I see there is a WD 40 Degreaser ,it says recommended for plastics but I haven't tried it.
As far as I know some mower shops use Simple Green Pro HD and it's good for an Ultrasonic cleaner ,I think Bunnings sell it but will cost a bit as you may have to buy 4 litres.
I'd just put 2 grease nipples into the plastic ,that way you can remove one when you use a grease gun on the other.
You could use a BSPT 1/8" - 28 grease nipple but you may not have a tap or a Metric M10 x 1.5mm Pitch.
