Free - Twin Disc MG-521 Troubleshooting Guide Parts for Twin Disc ® MG521 Marine Transmissions - Seal Section 1 Front seal for Twin Disc marine gear MG521 and MG527 . Price: $ 37.26 Qty: ^ Pictures In Stock Add to Cart 2 Rear seal for Twin Disc marine gear. . Price: $ 128.16 Qty: ^ Pictures In Stock Add to Cart Go Back Free - Twin Disc MG-521 Troubleshooting Guide