boiler inlet valve overflow leaking (w. pic)

Attachment 38782 (http://www.doityourself.com/forum/attachments/boilers-home-heating-steam-hot-water-systems/38782-boiler-inlet-valve-overflow-leaking-w-pic-drip.jpg)so, i had to let some water into my boiler pipes (as the PSI was low) . I opened the inlet valve and then opened the pressur evalve so the water could flow in. I closed the inlet valve compeltely shut but the overflow is now leaking. The inlet valve it welded so would be a cost to replace. Any suggestions : (should i just cap the overflow valve; or will this let additonal water into the pipes?) I included pic below