i broke my Lower A-arm should i change from plastic to metal

I thinck you're talking about a TA05 ? Yes , you should upgrade to aluminum. My TA05 is full aluminum and I like it allot. Never broke a single part and it gets raced hard.

Here's a link to my TA05 ( thread in another forum)
http://www.rcuniverse.com/forum/m_53...g%2Ccar/tm.htm

My nick name on the other forum also is Easy rider BTW

It still has the MM installed but the Lehner will be here soon ;-)