I had one set of spindle bolts work themselves loose on my 52 mini.
By the time I realised, I found they had made some serious cracks in the deck.
In the pictures you can see I cut out the twin layered deck and replaced that section with a single piece of similar thickness.
If your deck has 300hrs, even with rust, it should still be worth repairing, especially when you consider the price of a new one.
My mower had around 450hrs on it at the time. With 650hrs on it now and still going strong.