I studied almost all of the options last year when installing a new 124. I'm not sure I would call the stock unit an oil cooler or not. I'm sure it doesn't do very much and I wanted to do something that would give me some heat protection once we put the blower back on it. I spent the money and bought an Oil Bud and love it. ONly problem I have now is geet the engine to operating temp this time of year. Its a great product!
BigLew

I have Oil Bud coolers installed on both my 07 Softail Deluxe and 2010 CVO Ultra. In my opinion, it’s the best performing, non-obtrusive, most durable and well-constructed cooler on the market. Unfortunately, it’s also the most expensive (However in this case, I believe you get what you pay for).
I originally purchased one for my Softail. This bike didn't have a cooler to start with and I was concerned about the oil temps I was seeing on the gauge on my tank (normally around 235-240. But in stop and go traffic on hot days I was frequently seeing it climb above 250 and occasionally reaching 270-280 (very uncomfortable when you are sitting directly on top of the oil bag).
Before purchasing it, I researched and considered coolers from Jagg and MoCo. However, I didn't want to dirty the looks of my bike by mounting a large cooling element to the frame in front of the engine. So with some trepidation (mostly due to the cost), I decided to go with the Oil Bud.
So far it’s lived up to the claims made by Bud Clarke. Since installing it, the oil temp is now normally between 190 and 215. On a really hot days stuck in stop and go traffic it may climb to between 225-240.
Just like BigLew said, it seems to take longer to get the engine up to operating temp on cooler/cold days. The adapter housing has a thermostat built into it that is set to fully open around 190. My biggest concern now is getting it to at least 212 to burn off any moisture that may be in the oil.
After running it on the Softail for two seasons, I was completely sold on it. Because it gets the job done while not being in your face and because I wasn't happy with the performance of the OE cooler on my CVO ultra, I bought another one for that bike. So far its exceeded my expectations on this bike too.
The installation on the Softail was very easy.
With the CVO Ultra, I had to fiddle with it a little more during the installation on my bike. During the install, I added a 45 degree JIC adapter between the cooler adapter and oil line that runs to the rear of the cooler along the right side of the bike. Without it, the line came very close to the rear brake master cylinder linkage in my installation. I could have provided more clearance by repositioning the adapter, however doing so would have made it more difficult (but not impossible) to install wide band O2 sensors in the front exhaust header.
One side benefit that I noticed on both bikes is that the billet adapter shifts the position of the oil filter making it easier to replace.
However, when it comes to draining the fluids, while you can still access all of the drain plugs, you need to modify how you remove them so that the oil does not stream out and hit the cooler element making a mess. Bud has information regarding this on his web site. Basically, you need to make sure the fill caps are on tight and then slowly remove the drain plugs. This will reduce the flow. As the flow starts to slow, you start to loosen the fill caps to maintain the flow until eventually they are removed.
Bud Clarkes customer service and support is excellent. If you have any questions, give him a call.