If the leak only happens when the faucet is on, then it may not be the pressure lines. Am I understanding you correctly--does the water drip when the faucet is off, or on only, or all the time?
There almost always is some way to access the shower piping--as mentioned, an access panel somewhere on the wall behind the shower, close to where the shower control is.
'15 38RSSA Mobile Suites
'05 36TK3 Mobile Suites--retired but not forgotten
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