I've got a small crack appeared on one of my lower arms about 1.5" long up the side of the tension rod bolt holes.

As in the FAQ section:

 

http://www.300zx.co.uk/forums/showthread.php?t=22382

 

Only noticed cos I'm changing from poly bushes to the adjustable Powertrix rods.

 

Would it be safe to weld this or am I in for even more wallet pain?

It's not as bad as the ones in the pics in the FAQ thread.

What's involved in changing the lower arm? Big job?

Has anybody got a passenger side arm or maybe a pair?

I've put a post in the Wanted section but no replies in ages.

the cracking will get worse and eventualy fail, with mine when you braked to a stop you could here a horrible clunk, turns out when i did the passenger side one, i took the tension rod of and the holes in the arm fell straight through, so i just had a massive hole in them!!!!!!!!!!!! When you change them be careful that when you try to undo the nut where the ball joint goes onto the hub. the nut was so tight on mine the joint failed before the nut would undo, there for your left with the bloody thing just turning.