It was a critical procedure because, without it, Wiggle could not pass inspection and would never be allowed to drive again.
Patrick had worked as many overtime shifts as he could to help pay for the Rustectomy. Henry worked extra details with the Stop Light to bring in money. Cricket and Molly saved everything they could, and were ever so careful to buy everything on sale.
"When you wake up tomorrow Wigglebus, you will not believe how beautiful you are!"
Careful not to wake his sleeping patient, Michael, the Mobile Mechanic, a.k.a. "Bus Doctor" quietly put his tools away. He left a note for Henry on the driver's seat that read: WIGGLE IS READY FOR HER STICKER! GOOD LUCK! Then he quietly drove away.