Can't say I've heard this before. So citric acid should not penetrate the plastic?Vinegar penetration of plastic doesn't happen quickly. For me, it was a couple years of cleaning the wetsides by soaking in straight vinegar over night.
If you wish to acid soak your wet sides (or any plastic coated metal equipment, such as pump bodies or impellers), I'd highly recommend other acids that are less likely to penetrate plastic. Two acids I'd recommend that are inexpensive and readily available are citric acid (3/4 - 1 cup made up to one gallon), or diluted muriatic acid (diluted 1 to 10). Muriatic acid is available at HD and a five pound bag of Citric acid (a life time supply) is available from Amazon or eBay for 12 - 15 bucks.