Thats a wierd bruise from doing osotogari, my advice would be insted of grabing the lapel traditionally try and grab the lapel in the back of their neck, the elbow is higer and it works pretty well (for me at least).
About that elbow maybe you should see a doctor, whatever it is it may be getting worse without you noticing it, and whatever you do, I wouldn't go training (at least forcing the elbow) until thats 100%, its better to stop for a week then an entire month.
I think the elbow thing may have been a pre-existing condition. Whenever I lift weights (specially with overhead presses and cable pushdowns), past a certain load, I find it necessary to wrap my elbows. Doing osoto with the elbow on uke's chest probably was the needle that broke the camel's back.
The elbow is much better now, but as you suggested, I'm taking time off for the time being. I don't want to mess with that.
I think Yrkoon9's advice is very good. There are many different ways to enter and execute the osoto that I suppose would be called/viewed as "nontraditional kodokan".
BUT, you have to work with what you've got. Like has been suggested above I would try different hand positionings/handles and angles of entry to see if it makes a difference on the elbow. Good luck.