Before a quote, I'll go for a translation, as you ask.
Stressing the health theme, I've thought of:
omnia incurabilia sana sunt,
- omnia means all (things)
- incurabilia means incurable (things), hence omnia incurabilia: all incurable things. Note that the linked dictionary entry explicitly includes the meaning without remedy for the adjective.
- sana means healty (neutral gender, plural) or healthy things. (It is idiomatic in Latin to use adjectives in neuter and plural for this purpose: bona = good things, (all) what is good, mala = bad stuff, the bad, etc.)
- sunt is the third person plural form of the verb to be (they are)
All incurable things are healthy.
There is a number of variations you can choose from: both omnia and sunt aren't really necessary, they only affect emphasis or style. The word order isn't fixed either, at least regarding omnia with respect to incurabilia and the position of sunt: you could even go for something weird like sunt incurabilia omnia sana. But I think the first choice is the most standard, motto-looking one.
If you want to explicitly add the already part, you can insert iam as in omnia incurabilia iam sana, but I still think it is not as necessary as it is in English.
Alternatively, you could go for a more literal translation, like
Quae non habent remedium, iam remediata sunt
- quae plays the role of [the things] that...
- non habent remedium = have no remedy (pl.)
- remediata = remedied (neuter, pl.)
Update: I found a related (-ish) quote by Cicero. Many people prefer quotes over translations, even if they convey the idea more implicitly or indirectly. The fact that it was written millenia ago gives a sense of ancient wisdom. In that case you could use:
Cavebo quae sunt cavenda (Letters to Atticus, 1.17.10),
which translates to something like I will take care of what needs to be taken care of, implying that you don't need to seek cure for the incurable.
Regarding the pronunciation, there is a number of questions and answers about the subject in this site. In short, there is more than one accepted way to pronounce it, but if you ask me, the most important idea to have in mind is NOT to pronounce vowels as in English. Rather think of more phonetic languages like German, Italian or even Spanish. (Though strictly speaking it is accepted in English-speaking countries in some contexts —like legal Latin I think— to pronounce it more or less as if they were English words).