lay z spa pump heater stripdown error E02

This is a full strip down (nearly) of the whole bestway #54154 heater filter pump.
I"ve been dogged by E02 so often now it was time to take control.
A video containing the final fix is here • Lay-z-spa hot tub E02 ... but please stay with this video to learn the total strip down.
I'm being asked loads of questions, which I'm happy to answer, but...
PLEASE NOTE: I'M NOT AN EXPERT! Any advice, comments or actions taken are NOT to be considered as expert advice. If you take your pump apart for any reason at all you do so on your own and YOU ARE LIABLE, not me. Thanks
The magnetic reed switch (no) 59025-90B 1632G.
I couldn't find an exact replica, but Farnell.co.uk had the same type of switch, just a slightly different spec.
the sensor is 59025-1-S-02-A REED SENSOR, PLASTIC BARREL, 6MM, NO (normally open) : but check yours with a magnet and an Ohm meter before ordering a new one.
I'm told 60% of the fails are due to magnet failure. (I don't know how true that is)
Please read the comments for other questions... your answer may be in there.