I washed my Mattes half pad without Melp :eek: but with human hair conditioner applied first, came out fine :), I would say wash when you think it needs washing
I had the same issue with the Albion ages ago, in hindsight the seat was too deep for me for a gp, I've just bought a new saddle and the K2 was an option again, still too deep for me.
How about a slightly different approach, if I were joining a gym or employing a fitness coach, I would expect to have a new client sheet, filled in. Name, DOB, height, weight, health issues, what I want to achieve. Why shouldn't that be part of riding instruction too, one for horse too, a way...
Some ex racehorses and trotters I have experienced can be quite institutionalised if they have been racing for a long time and find anything outside the framework they are used to quite stressful because to them everything is new/different/worrying, even to the point of a change in surface...