There is one auto parts here that sells rolls or measured lengths of o-ring stock, find one in your area tell them the diamater and application to determine the composition you need, cut it to length with a sharp razor and super-glue the ends together. If your unsure about the DIA of the squished one you have, measure the hight and width with a caliper and add the two together and divide by two.
If you cannot find someone that has the o-ring stock, find a local machine shop in your area and ask them if they have it or know someone that does.
