cracked alum. block

i have a european 500SEC with a small crack in the engine block near the oil filter housing (happened in a wreck). this happened before i bought it and they epoxied the crack which seemed to work fine for approxinately 100,000 miles (now has 139k). howver, it's leaking more and accidentally overheated which may have blown the head gasket since it now runs pretty hot.......i'm not driving it beacause of this.

my question is how to fix this. should i just shop around for a used engine? the present engine has new timing chains and injectors, but i worry that perhaps the head could have sustained damage (although it runs fine....just overheats). is it possible to weld the aluminum block (and then just fix the top end)? i have been told (hypothetically) that you can't weld those blocks even though it would be a fairly small area. i have taken very good care of the engine since i've had it (ie- frequent oil changes using synthtic oil) and would rather fix what i have if possible. on the other hand, i don't want to spend more than about $6,000 to fix it when it appears that i can get a used engine for less than $2500.

i'd appreciate any advice.......thanks

fred