Free - Twin Disc MG-521 Troubleshooting Guide Twin Disc MG 521 Marine Transmission Parts - Seal Section Loading... 1 Front seal for Twin Disc marine gear MG521 and MG527 . Price: $ 46.61 Qty: ^ Pictures In Stock Add to Cart 2 Rear seal for Twin Disc marine gear. . Price: $ 157.20 Qty: ^ Pictures In Stock Add to Cart Go Back Free - Twin Disc MG-521 Troubleshooting Guide