Without reading the plethora of replies DX, as an airline pilot and PPL weekender, albeit less and less frequently now (the pay's not all that) the answer is quite straightforward to me.
If a pilot needs assistance, 121.5 is absolutley fine. And pardon the vocab, but bollocks to anyone else trying to be officious on guard. If a pilot needs help, he needs help. It could well be a young 18 year old on a solo nav ex, last thing he needs to hear is some idiot with NO COMMON SENSE (!!!!!!) arguing the toss about who needs help and who doesnt. Let DnD sort that out.
Guys if you need help, call them. Rather that than an event that could ruin your day. We can all argue the toss in the bar afterwards.