I would suggest that you take a voltage reading at the glow plugs immediately after turning on the key. Once you KNOW that there is 12 volts at each of the plugs, THEN replace the plugs.

Taking resistance readings of the plugs do not tell the whole story. I have had plugs that had good resistance readings but would not get the job done.

If there is 12 volts or so at each plug, replace the plugs. If there is NOT, then work toward the glow plug relay.

Any yes, a fresh engine or even an old engine with good compression and everything right will start right up in warm weather. Sixty degrees would require a few seconds of glowing.

Good luck,