Alif, the SL most definitely has the relay. I finally got a look under my hood, and it is located in the covered corner on the passenger side. It is very easy to spot there, and has a red fuse right on top of it. Check or replace the fuse then relay, especially if your ABS or Top lights are on. It worked for me. As far as your hard starting after sitting for a while, I have the same thing, as well as a few other members and I think it's called vapor lock. I just live with it and remember to hold the throttle down when starting the vehicle warm.
'90 500SL (sold)