With regard to your question about there being a skirmish of any note which involved Gracie's Brigade, I haven't been able to find anything from late June of 1864 until mid-March of 1865. During this time they occupied a par of the Confederate line along the eastern face of the Petersburg defenses which became known as Gracie's Salient. General Johnson reported regularly regarding the number of deserters and casualties in his division, but never mentioned anything that would rise to the level of a noteworthy action. There should be something in the Brownlee service record to indicate what happened to him.