The lord helps those who help themselves
Your parts manual link click the green text
You will see there were 2 carbs fitted to this mower depending upon the manufacture date
Date code = serial number minus the last 2 digits
so you will see there are 2 rebuild kits .
I seem to be unique as I rarely have any problem with these Nikki carbs other than freeing a stuck solenoid plunger and cleaning the float needle seat so the only parts I really use are 137 in the diagram , the rubber seals.
Occasionally the O ring on the main jet fails so occasionally I have to replace it as well, sold only as a kit with the jet.
When assembling , a very thin coating of RUBBER grease will hold the complex rubber seal in place.
If the main jet falls out when you tip the plastic bit upside down then the main jet O ring has failed
If it does not fall out, leave it in there as removing it usually damages the O ring
Because the main jet lives in a plastic housing it rarely corrodes because there is no electrolysis .
Note you will see 2 totally different styles of rebuild kits on Scammazon & Evilpay.
Usually with a float and the plastic main jet holder .
One will have a fuel inlet O ring as a separate item & the other has it as part of the rubber seal
99.99999999999999999999 % of these kits will be defective or contain a mix of parts for different carbs or a mix of parts for the original carb & the knock off carb ( float is smaller ) so buy genuine or get them from a REAL Mower parts shop .
People always whinge about these carbs but they leave the Walbros for dead for reliability & ease of service so I am sure that the whingers are just cheap & bought one of the defective / wrong parts kits off Evilpay/Scammazon for $ 5 so in reality are just victims of their own cheapness .
Do not blow up the main jet holder with your air duster, even if you have done the right thing and wound down the air pressure to < 20 psi or you will sent the main jet into low earth orbit, never to be seen again.