This is one of the less-common ways a cylinder head gasket can leak. More commonly the coolant will get sucked into the cylinder where it is burned, then appears at the tail pipe as white smoke. Coolant leaks into the oil in about only two or three percent of head gasket failures.
You did not list the engine size, but the Intrepids never came with four-cylinder engines. They only have V-6 engines, so there will be two cylinder head gaskets. It is customary to replace both. No conscientious mechanic would replace just one since the second gasket is just as old and just as likely to fail. Replacing them is a really big job; not one you would want to do a second time. This is not a job either for most do-it-yourselfers. Special tools are required, and proper "surface prep" is critical to give the new gaskets something to bite into and seal. Many mechanics are not qualified to do this type of engine work, and I would only recommend an experienced, competent do-it-yourselfer attempt it.
Your best approach is to visit a few independent repair shops that regularly do engine work, and get some estimates, but be sure when comparing them that the same things are included. Once the job is done, the oil will need to be changed. Be sure the oil and filter are included in all the estimates. Given the mileage you listed, most mechanics are going to recommend a new timing belt or timing chain to insure the quality of the repair. If that is included in one estimate, be sure it is included in any other estimates you are comparing.
Be aware that antifreeze in the oil will melt the soft first layer of engine bearings. That will lead to a catastrophic engine failure where it is likely to be less expensive to get a used engine from a salvage yard. To avoid that, have the problem repaired and get that oil out of the engine as quickly as possible.
One thing that can lead to head gasket failures is failure to replace the antifreeze every two years. Corrosion inhibitors, water pump lubricant, and other additives wear out in about two years, then acids will begin to form in the coolant. That can lead to corroded radiators, heater cores, and head gaskets.
Here is a link to an article about cylinder heads that might give you more information:
Sunday, October 14th, 2018 AT 9:28 PM