Gaco as a company no longer exist, we were many years ago Distributors for Gaco. Our equivalents list endorse that the MIS numbers were just standard rubber covered oil seals with a single lip. This is the direct equivalent. 

Nitrile rubber covered oil seals for temperatures up to 110c.

R23 Oil seals have an extra wiper (dust lip or twin lip). These seals have rubber Nitrile OD with metal insert, primary lip and an additional dirt/dust lip (sometimes called a wiper) moulded with the overall seal width. They can also be referred to as "Semi dual" lip type, as the name suggests they help prevent the ingress of dust/dirt into the primary lip area.