I have used up my previous F1-OPT (post completion) to do be a research assistant with my current advisor. I could do a pre-completion OPT but as per the website you linked me to:
"If the student chooses to engage in pre-completion OPT, he or she may not work more than 20 hours per week while school is in session, but may work full-time during his or her annual vacation and other times when the school is not in session."
So I can't go on doing a job on pre-completion OPT forever.
IANAL, but I don't understand why you would have had to use your F1-OPT for an RA position.
I am not recommending F1-OPT forever obviously. But, it would buy you time until you find someone willing to sponsor and H1B. Things are much easier these days.
"If the student chooses to engage in pre-completion OPT, he or she may not work more than 20 hours per week while school is in session, but may work full-time during his or her annual vacation and other times when the school is not in session."
So I can't go on doing a job on pre-completion OPT forever.