hi,
crank end play at 77k? very unusual indeed,never seen that before on a silver series engine and i have seen them do well over 300k miles no problem.
crankshaft end play is normally due to worn main bearings on the crank which have shims that should limit end float within a given tolerance, silver engines use a two piece carrier plate arrangment that the crank runs in. however it is a very tricky thing to measure with the engine in the car and the crank bolted to a pressure plate for the clutch or a torque convertor on a auto. how was the play measured? where did they mount the DTI to get the reading? if you have a manual box then when someone pushes the clutch in and out you can sometimes see excess end float by looking atthe end of the crank and looking for forwards/backwards movement,but this can be hard to see.im not saying the crank hasent got excessive end float but i would be very sceptical, if leaks are your problem than its more likely the breathing system is blocked or the crank surface that the seals run on is damaged etc..
if at the end of the day crank float is to blame then im afraid you cant really do anything about this due to the design of the volvos bottom end so new or recon engine would be the answer.

regards
steve.