This is another one that already exists:
Ownership, simplified. Meet Custodian: the go-to app for car enthusiasts.
app.custodian.club
I guess the issue with all of them (a bit like Photobucket and Flickr or the media streaming apps which went out of business) is that your information is only collated so long as the website exists. It can easily disappear at the drop of a hat.
Unless you are offering some way to authenticate the user inputted documents or can link up all garages (both main dealer and independent), I cannot see what you are offering is differentiated from existing, free, offerings in the market.
And these days with scanners Acrobat and Photoshop, it is too easy to fake digital or hard copy documents.