I have two SL's A 85 380 and a 90 500 SL. The 90 is the difference of night and day compaired to the 85. More creature conforts and a lot more power. I have no regrets in purchasing the 90. I wish I had purchased it sooner. I would recommend you purchase the 500 over the 300 simply because of the power. It appears that your SL is in perfect condition. You may want to keep it.

Wayne