I would definitely want a mechanical solution rather than an adhesive. I'd assumed you'd want a washer that had an inner flange to address the diameter difference. Easily done.
The 3D printer I have access to at my work is a normal (FDM? Something like that) hobbiest type, it is basically an X/Y plotter with a hot glue head on it that prints layer by layer from the bottom up. I hope to someday delve into other styles like resin or powder printers, but that's not happening anytime soon.
It prints in ABS plastic, the same stuff Legos are made of. It will withstand the sun a bit, but longterm exposure certainly takes it's toll. The beauty of 3D printing is that once it wears out, you just print another and substitute.
There are also companies like www.shapeways.com
that can 3D print things in all sorts of materials, even metal. I haven't priced their services in a while, but it always seemed very affordable. You just provide them with a digital file, a credit card, and they make and ship it to you. Kinda cool.