I've NEVER seen that before! Chassis, yes. Rear crossmember, yes! But gearbox crossmember?? Dread to think what your chassis is like
seen it several times... gearbox cross member has two flat plates that are perfect traps for water, seen so many good chassis completely rotten in the area when the cross member is removed.... really crap design.... and so simple to solve... rust treat, paint, waxoyl n finally copper grease n it'll never re-occur..
cheers steve