Check list for rust areas on W210 and independant inspection?

Tomorrow I should get my 1999 E240 back after three weeks after having a 4 wing replacement due to wheel arch bubbling paint. Knowing that the Mercedes repair agent will not themselves undertake to identify such flaws I
would like some opinions as to how in the future to go about:
(a) getting educated as to where ALL the trouble spots might occur in this W210 model?
(b) should I pay someone for an independant inspection report? My concern is that a further similar problem might be identified and by that time Mercedes-Benz might have withdrawn their 10year (or is it 30 year??) warranty on paint?/rust?/perforation? (I don't know what it really is or what the rules are)
(c) Can a Waxoyl or similar treatment halt rust spread on a 6 year old W210 assuming that no further rust is externally visible?. Okay so I'm not confident on this reply 8:(

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