[sdiy] capacitor ID please

[markus]

in an old tube console stereo amplifier from the 60's i was surprised to 
find only one large aluminum canister-type cap. it reads :

40MFD 400WV (half-circle icon)
40	400	(square)
40	400	(triangle)
200	50	
1013	6137 FP
"stereo 33" sticker on top of the canister


what kind of cap is this? how do i determine if it needs replacing ? what 
would be a good replacement ?

TIA
mark scetta