My 2001 Mirada had a couple broken studs (one on each side). They were on my "watch" list for several years, never go worst, never leaked. but I know they were on borrowed time. When I sold the MH, I showed them to the buyer, and told them to keep an eye on them as they needed to be replaced.
My "New-to-Us" 1999 Southwind has one broken stud on the drivers side. Here are my thoughts:
The OEM studs (as crappy as they were) lasted almost 20 years. Even if I replaced the studs with the same OEM crappy studs (which I wouldn't), they should easily last another 20 years. Way, way beyond my plans to keep the MH
Next spring (or maybe this fall), I plan on removing the manifolds and installing all new new studs and gaskets. I'm doing this for my piece of mind, and its a selling point in a few years if I decide to upgrade.
This is a $15k coach, spending 2k to get a meager improvement in performance is not in my cards. I looked at aftermarket headers, tuners, etc. Even if they produce the gains their sales literature promises, the gains are so small (if they really are there) that even if I kept this coach for 20 years, I'd never recoup the cost, and it would do little to nothing to add resale value to an OEM configuration.
I can spend that 2k on other, more measurable, improvements, i.e. new shocks, tires, airbags, new COPs and plugs, etc.
To get the maximum HP out of the 300 hp, I make sure the maintenance items are up to date, i.e. clean MAF sensor, replace air filter.
The Cat Converter on mine was partially plugged and the PO removed it. I suspect on older MHs of my vintage, dealing with a partially plugged cat converter will improve performance more than any aftermarket header or tuner.
This is all my opinion and the direction I'm going...