Hello
If your P21 rudder is similar to mine, it is quite easy to lift the rudder blade by working the tiller up and down a few strokes as you maintain tension on that uphaul through the cleat. (Like a pump action)
The downhaul is held in the rudder blade by a simple knot which is covered over with a dab of resin. It might need drilling/breaking out step by step with a 6mm drill in order to dig out the old ‘plug’ from one side
Hope this helps
Lindsey P21 Amy (Brancaster)
PS I am a mere 75yr old - the owner of P21 Sea Fever was sailing into his mid 80s (almost every day during the season!) Ideal yacht for pensioners!!