Unfortunately, most of them. The issue here is the notion of "single use". You have to consider that a single encryption session might be longer than your random 3072 prepended bytes. So RC4 output bytes 3073 onward will be (presumably) XORed with the genuine plain text. If you then aim to encrypt 1GB of hospital patient records including weeping diseases, HIV status and religion, all the many identified long run biases will bite you hard. Initial byte drop won't help other than to reduce the most extreme biases. The other still very strong biases will be there downstream.
You might also fall foul of a weak key state if the keys are random or perhaps lacking sufficient entropy. They exist. There are so many short and long run biases that it's just simpler to refer you back to the Q&As tagged with RC4. Are there any long term RC4 bias based exploits? is just a single example. And of course no (Does this fix)RC4 answer is complete without Why is writing your own encryption discouraged?
Yes, RC4's problems are well understood, but if you review the RC4 answers you'll see that RC4 is fundamentally broken and so far no tweak has managed to restore faith in it. To quote someone earlier, "Just Say No to RC".