The Mk-10 is not where near old enough to be considered Vintage, the R190 for sure isn't. In any case, you have a very solid modern regulator that will hold it's own with most any on the market today and outlast most of them if you take reasonable care of it. Don't worry about the parts price, that is reg salesman BS to get you to buy a new reg. Sure you will pay for parts but that reg does not need service more than evey 3 or 4 years, most will go longer. So what if you pay $50-75 in parts every 3 years, you also save the $75-100 in labor cost each year you skip a service that would be mandatory if you buy new...and if I remember correctly, SP now requires you to not only purchase a reg but a BC as well to get the parts for life. Better yet, learn to service it yourself and save the labor cost as well. This board has a great bunch of SP DIYers that can help you along. Unless you have zero tools, the few special tools you need are easily covered buy the cost of one official service....and there is no garrentee that that will be done correctly.
What I would do is to sell the R190 and find a good 109 second to replace it with. Now you have a great second stage to go with the first. Service the entire set and dive it.
I just checked the prices of MK-10 kits on Vintage Double hose- MK-10 is $15, the 108 and 109 kits are $5 which makes the parts cost of a DIY service $25 every few years...find a new reg that can match that. Granted, these are aftermarket parts but quality orings are quality orings reguardless of who sells them to you.