$4K, car looks mint, service records, new tires, exhaust, battery, and brakes?
If it attracts your attention, I would go for it.
BUT, do check it over for rust and be prepared to spend some big money on the Transmission.
Still, the transmission issue might just be a simple fluid level check, linkage, or the Modulator Valve.
If you are a DIYer, the AC could turn out to be an easy fix - both of mine I did myself, one $400 for a new AC Compressor, and the other $100 for a high pressure hose.
Check the condition of the Soft Top - if it needs replacing plan on $400 if you DIY it, or $1500 if you hire it done.
Its good attributes since you used the word "mint" is that the paint and interior only need perhaps waxing and dolling up. Not having to repaint is a big expense you are avoiding.
New tires avoid a $500 to $1,000 expense.
My 560SL has 190K miles, I've seen really nice looking ones with 300K miles, and one person on this forum posted one with 700K miles. If its been well maintained, and a lot of the miles are road miles to and from Florida, that engine is probably A-OK.
Still, be prepared that you will need to spend some more after you get this 450SL, and even if you purchase a low mileage SL you still need to be prepared to spend more money. DIYing on an R107 is a great hobby and adventure for someone with DIY skills and some time on their hands.