Once was enough. Is it ideal, well no. Does it matter? I wouldn't worry at all. The stress cracks that have shown up over time on the OP's stem are most likely from overtorqued and/or unevenly torqued bolts, which the majority of people end up with. We're not talking about piston sleeves and valve seals in a motor, we're talking about a stem that clamps onto a round metal bar with 2-4 bolts and 0.6mm difference in diameter.